All knowledge comes about by means of an image.
It is erroneous to think that an image is a mere tool, which human intellect needs because it's weak and can't function without the cooperation of the senses. Instead, the image is an essential part of knowledge itself, since all knowledge is an assimilation by which the knowing subject intends to become in a sense, through the likeness, identical to the known object. Without an image, even in God there can be no knowledge.
The image in divine knowledge is divine Essence.
This can't be otherwise, for there's no distinction between God as a knowing subject, God as a known object, and God as an act of knowing. Divine knowledge, being a pure act, can't be essentially distinct from divine Essence, which knows Itself. God is the highest perfection of being, so we can't accept any potentiality in the act of knowing: God is his act of knowing. On the other hand, there can't be in God any potentiality to be known. He is actually known.

{{In the philosophy of Plotinus, duality between the knowing subject and the known object is incompatible with the fact God is one and undivided. Therefore, it's not the highest Being that knows, but the second principle of Being, the Nous, which proceeds from the first and single Being by immediate emanation.
Later philosophers like Fichte and Spencer have the same opinion that the opposition between intellect and object is incompatible with the absolute identity in divine Essence.

Saint Thomas apparently did know this difficulty, but he didn't largely deal with it, probably because it lost its right of existence after the elaborated theses about God's identity and knowledge.
Yet, we repeatedly see that Saint Thomas elucidates why the distinction between the intellect and the object of knowledge needs not be real. Indeed, this distinction is only real in man (and animal), since he is a creature. The distinction is an imperfection divine knowledge can't be subject to:
"Because in God, who is Actus purus, there is no potentiality, the intellect and the object of knowledge must be one and undivided in every respect."
"The organ of sense and the intellect are only distinct from the object we perceive with our senses and our intellect because both have a potentiality (to coincide with each other) that's not yet act."
The real distinction between the knowing intellect and the known subject finds its origin in the circumstance that the potentiality (to coincide with each other) is not yet act. This is essentially an imperfection that doesn't make all knowledge defective, but only knowledge in creatures. Divine knowledge must be exempt, because it doesn't have potentiality, but is pure act. "Although the concept of knowledge presupposes knowing and the knowing subject and the known object, these three things needn't be really distinct."}}

What is the object of divine knowledge?
God knows Himself in the first place.
Whenever a subject knows something, it knows in itself an object that is present according to its actual faculty to be known. Because divine Essence is perfectly incorporeal, it has an absolute faculty to be known. It is knowability itself. Furthermore, being Actus purus, God is free from any passive potentiality. He doesn't essentially need an intellectual concept or idea by which a knowing subject can actually know Him. On the other hand, God's infinitely knowable Essence coincides with His intellect that actually knows. Since the unity between the knowable object and the knowing subject is perfect, the knowledge God has about Himself must be perfect.
"Because there is no potentiality in God - for He is pure act - therefore His intellect and the Object it knows must be one and undivided in every respect ... So He knows Himself by Himself."

God also knows the other things He's calling to existence outside Himself as their first cause.
We can deduce this knowledge from the knowledge He has of Himself. If God, whose intellect is infinitely pervading and whose Essence is infinitely knowable, is seeing perfectly through Himself, He must also know all of his own causality. Divine causality, however, doesn't only stay within God's immanent life, which man's natural intellect can't know, but it also ranges over the things that divine omnipotence calls into existence by creation.
God is knowing Himself directly, because if God should know Himself by means of something that's not Himself, He would receive a perfection from outside. So He is seeing through all other things in the image that's his own Essence. This Essence is bearing in itself the perfect likeness of the creatures, because the distinct perfections of being we find in the creatures in an inferior and relative way, are perfect in the first cause. It's not a likeness according to nature, nor the formal likeness of, for instance, two people who are essentially equal in some ways. It is the likeness of reflection. Although the consequence as an image of the cause is present in the cause, the cause doesn't fully express all of its properties in its consequence, but it only reflects them. This likeness of reflection is also existing between the transcendental first cause and its imperfect representation in creature. In so far as the creatures are sharing in some, always finite, degree, the properties of divine perfection, and are weak reflections of the inexhaustive riches in God's Essence, they all find their highest and most understandable likeness in the first cause. That's why divine Essence, which created beings can imitate in countless gradations and nuances, is bearing the character of a divine idea of knowledge, by which God is seeing Himself as imitable in any creature in a certain finite way.

In God, everything is eternal and unchangeable. So this holds for His knowledge and His act of knowing as well. But which relation has divine knowledge to distinct creatures who are living in times far apart? Must the intellect be tied to time itself, in order to be able to know temporary things?
This is an obvious question, and man's imagination tends to answer in the affirmative.
However, Saint Thomas answers in the negative, and his answer is both sufficient and short.
"God's knowledge is the cause of all things. In fact, divine knowledge is in proportion to the created things as the knowledge of an artist to his products.
In reality, there is a radical contradistinction between the knowledge of things in ourselves, and the knowledge of things in God. In our knowledge, we're completely dependent on the objects we know. Indeed, the object of knowing determines the character of our knowledge, and excites in us the interest for new objects; it teaches us a reality that had hitherto stayed hidden for our mind. But no creature can ever enrich God's intellect, which is completely independent of the creatures, whereas, on the contrary, the creatures are in their very existence completely dependent on God's intellect. For God is the eternal and unchangeable Maker of the beings He calls to existence by creation. That's why the things contingent that have been or are or shall be can't ever predetermine God's intellect, but these things have been, are or shall be because the eternal and unchangeable knowledge in God is realising them in a certain order of time.
Because eternity in God doesn't know any succession of past, present and future, everything in Him is actually present. In his eternal Now, He knows the creatures together with their temporary duration and their temporary order. It's a peculiarity that belongs to creatures as such, that they are distinct from each other according to time, since they occupy an own distinct place and a certain duration of time by the composed character of their essence and existence. But the circumstance God knows the creatures together with their place and duration, can't bring about in divine knowledge any temporary successions or local distinctions, because divine intellect isn't dependent on its created piece of art, but the created piece of art is dependent on divine intellect.

God knows the past, the present and the future of his creation in his own incorporeal and unchangeable Essence. Therefore, He sees everything in the full daylight, whereas, for example, our human knowledge is jumping from one moment of time to another, and always perceiving the past moment less clearly, and the future moment in a mere fog of conjecture.
Saint Augustine called, for good reasons, the all-penetrating knowledge of God a scientia matutina - a daybreak knowledge - as opposed to the evening knowledge of man, which is very colourless and dark indeed.
"In comparison with the knowledge of the Creator, the knowledge of the creature is like the twilight of evening ... The knowledge about the creature in the creature is, so to speak, paler than the knowledge in God, from whose wisdom the creature proceeded like from the plan of the artist."

God's will

If we start from the incorporeality of God's nature and conclude God is an intellectual Essence, we also have to credit him with a will. Because intellect and will are inseparable from each other. Will is an intellectual striving, it's unthinkable without intellect. But intellect judges of good, and it's unthinkable that it wouldn't strive for good. Intellect and will are equally unlimited in their potentiality. They both have being as their object. The only distinction is that will is aiming at good, whereas intellect is aiming at truth.
So, because there is in God an intellect, there must also be a will. Saint Thomas says:
"In God there must be a will, because there is an intellect. Because will is a consequence of intellect. As all things of nature thank their actual being to their form of essence, so intellect thanks its actual knowledge to its intellectual form of knowledge. Now any thing is exhibiting with regard to its natural principle of form its bent to strive after it as long as it doesn't yet have it, but to settle down as soon as it does. In fact, this holds for any natural perfection, which is a natural good. We call this bent for good in things of nature that don't have an intellect: natural striving. Therefore, our intellectual nature must also have a bent to the good it perceives in its intellectual form of knowledge. Indeed, the intellect is striving after it as long as it doesn't yet have it, but settles down as soon as it does. Both of these two functions belong to will. Therefore, in any reasonable being there must be a will, as there is a faculty of sensory striving in every sensory being. So there must be a will in God as well, since there is in Him an intellect. Just as God's knowing and being are one and the same thing, God's being is also the same as God's will."
We call will the intellectual faculty of striving, but, this way, we use a name that can't but poorly express the essence of will. Because, although this striving is for us the most striking deed of will, it is in itself an imperfection that clearly illustrates the defectiveness of human will, but leaves its perfection in God almost completely in the dark.
The first function of will, which is dominating all other functions, is love. This love has as spiritual a character as the knowledge it's leaning on. All other deeds of will, like longing and fear, joy and dislike, are presupposing love for good, which may be present or absent, easily attainable or threatened by a prevailing evil, but is enchanting anyhow.
It's true God can't strive after a good He doesn't possess yet. But is this an imperfection?
Hereby, God's will is even more perfect, because God's love isn't weakened or restrained by any distance in space of time from the highest good it's enjoying in eternity.

The good that God is loving and infinitely enjoying in eternity is his own divine Essence.
God knows himself as the Bonum Subsistens, which doesn't bear in itself any imperfection, and which all other things are dependent on with respect to the good of their essence and existence.
Highest good isn't only worthy of all love, it also irresistibly evokes love in the intellectual subject that knows good in its whole fullness. As man must of natural necessity wish his happiness, because his intellect perceives that happiness contains all good and no evil, so God must of necessity love himself, because with his infinitely pervading intellect He sees perfectly through his Essence and acknowledges it is the subsisting good that exists on its own strength and has no adherent shortcoming or imperfection whatsoever.
God's love of himself is free from any egoism; it is a pure and sacred love.
Egoism is unjustly preferring oneself to others. The egoist seeks himself at the cost of some other. But the love God has for himself can't be unjust anyhow. God is loving what merits highest love and doesn't violate the rights of anybody. In fact, such a violation is impossible. Because the goodness of things outside God can't possibly deserve a preference above God's goodness, since creature is only a weak shadow of divine Essence and thanks all its good qualities to the superior good of its Creator.

God also loves all things outside Himself.
The relative good of creation, too, is enjoying the benefit of divine love in proportion as it's perfect.
Perhaps, it may provoke astonishment that divine Essence, which is entirely sufficient for itself and perfectly satisfying divine love, can show sincere interest and devoted love toward things that, in comparison with God's perfection, sink into nothingness. Nevertheless, it's an undeniable fact that good is naturally communicative and true love can't be insensible to any good, be it ever so small.
In God, good is infinitely communicative and love has the most universal character.
Whatever is good, naturally wishes to communicate itself. In the order of nature, we can measure the degree of perfection of a thing according to how communicative the thing is. As far as we can perceive, the sun is a more perfect celestial body than the moon; it is spreading more refreshing light and radiating beneficent warmth; the full-grown plants and animals are propagating themselves and serving each other, especially man; and man himself, if he is honest, is naturally devoting himself to the apostolate of good. But all these things, sun, plant, animal, man, are in their turn manifestations of God's communicative goodness.
Good is the object of love. Love, that's leaning on a clear insight in all good, can't exclude any good; it is sensitive to any good.
God is highest love. The relative good of all creatures is included in God's good as its cause. Therefore, God is willing and loving in Himself the creatures as reflections of his own perfect Essence. As divine Essence is the first, own and moulding object of God's intellect, which knows and fathoms all other things in the same divine Essence, so God's good is the first and specific object of God's will, which loves all creatures in His good, in so far as they are finite representations of the infinite Cause. Saint Thomas says:
"God is willing the other things because of his own goodness; not in such a way that He could enrich himself with these things ... but in such a way that He enriches these things with his own goodness in some degree."

However, God's will is completely free, and not in any sense dependent on creation.
The universal law of God's entire outward efficacy is: the Creator is communicating himself in creation, without winning or losing anything, and He's making each creature dependent on Himself as to its being, whereas He's not making himself in any sense dependent on the creature. The creature is a finite and defective image of divine cause; it's God's being, but restricted by contingency and limited by space and time. One Blondel said: "Si peu que ce soit, l'Etre fait donc les êtres pour qu'ils soient, peu ou beaucoup, d'autres lui-même."
God doesn't need these weak and inferior reflections of his own Essence. Being the Bonum Subsistens, the good that is existing on its own strength and by its own strength, God is entirely sufficient to Himself.
Therefore, nothing compels God to the deed of creation. God's will of creation is a free will. Although the created cosmos is eloquently testifying the highly communicative goodness of God, yet divine will is as perfect without the good of the creatures as with this good, and divine love needs not extend to the beings it can call to existence in a generosity we can't understand.

{{Several philosophers, representatives of scholarly optimism, thought God had to create out of an inner necessity.
Plato, Plotinus, Leibniz, and others, each by their own conviction, ascribed to divine Essence a primitive power that of natural necessity is revealing itself in the most perfect creation we can think of. Hence, especially with Plotinus, the cosmos is taking the character of a divine emanation, as, for instance, light is an emanation of the sun. Meanwhile, this way God's will is losing its freedom before the things created: the natural gift we're bearing within us, and which we are ourselves, wouldn't be a free gift of love; it would be the uncontrollable eruption of God's good, that can't but be fruitful.

Cajetanus refused this opinion because of philosophical considerations.
He called attention to the fact reasonable beings have the perfection they can freely communicate themselves to others. Just like perfection, however, freedom allows gradations. If a reasonable creature would voluntarily isolate himself, communicating nothing of his own riches to others, it would miss its mark and this would be an essential shortcoming. However, divine perfection is infinite in every respect. It doesn't allow augmentation or restriction. If God didn't wish to create, He would stay all Himself, nor have any shortcoming. Because God is sibi sufficiens - sufficient to Himself.
Garrigou-Lagrange comments as follows on this opinion of Cajetanus:
"La liberté divine en effet n'est pas l'indifférence dominatrice d'une puissance ou faculté; c'est l'indifférence dominatrice de l'acte pur à l'égard de tout le créé. On comprend ainsi que l'acte libre divin n'est pas une action accidentelle et contingente, surajouté à l'acte par lequel Dieu s'aime nécessairement lui-même. Il n'y a en Dieu qu'un seul et même acte d'amour, qui se complaît nécessairement en la bonté divine et conserve une indifférence dominatrice à l'égard de tout bien créé, qu'il appelle ou n'appelle pas à l'existence selon son bon plaisir."}}