Thomas Aquinas

“ Much less does the third movement lead to perfect knowledge: for even the angels themselves, by the fact that they know themselves, are not able to arrive at the knowledge of the Divine Substance, by reason of its surpassing excellence. Therefore the soul of the first man could not see the angels in their essence. Nevertheless he had a more excellent mode of knowledge regarding the angels than we possess, because his knowledge of intelligible things within him was more certain and fixed than our knowledge. ”

“ Wherefore no one who sees the Essence of God can willingly turn away from God, which means to sin. Hence all who see God through His Essence are so firmly established in the love of God, that for eternity they can never sin. Therefore, as Adam did sin, it is clear that he did not see God through His Essence. ”

“ Therefore neither could Adam's soul.
I answer that, The state of the human soul may be distinguished in two ways. First, from a diversity of mode in its natural existence; and in this point the state of the separate soul is distinguished from the state of the soul joined to the body. Secondly, the state of the soul is distinguished in relation to integrity and corruption, the state of natural existence remaining the same: and thus the state of innocence is distinct from the state of man after sin. For man's soul, in the state of innocence, was adapted to perfect and govern the body ”

“ Further, individuals of the same species have the same way of arriving at perfection. Now other men have not, from the beginning, knowledge of all things, but they acquire it in the course of time according to their capacity. Therefore neither did Adam know all things when he was first created.
Objection 3: Further, the present state of life is given to man in order that his soul may advance in knowledge and merit; indeed, the soul seems to be united to the body for that purpose. Now man would have advanced in merit in that state of life ”

“ Thus in a sense his knowledge was midway between our knowledge in the present state, and the knowledge we shall have in heaven, when we see God through His Essence. To make this clear, we must consider that the vision of God through His Essence is contradistinguished from the vision of God through His creatures. Now the higher the creature is, and the more like it is to God, the more clearly is God seen in it; for instance, a man is seen more clearly through a mirror in which his image is the more clearly expressed. ”

“ Hence we see that when the natural power of judgment is free we are not deceived by such images, but only when it is not free, as is the case in sleep. Therefore it is clear that the rectitude of the primitive state was incompatible with deception of the intellect. ”

“ If any object, as some do, that he was not guided, when tempted, though he was then most in need of guidance, we reply that man had already sinned in his heart, and that he failed to have recourse to the Divine aid. ”

“ Were anything presented to the imagination or sense of the first man, not in accordance with the nature of things, he would not have been deceived, for his reason would have enabled him to judge the truth.
Reply to Objection 4: A man is not accountable for what occurs during sleep; as he has not then the use of his reason, wherein consists man's proper action. ”

“ God was seen without this second kind of medium, but not without the first kind. For there was no need for the first man to attain to the knowledge of God by demonstration drawn from an effect, such as we need ”