Objection 1. It would seem that Adam, in the state of innocence, saw the angels through their essence. For Gregory says (Dialog. iv, 1): "In paradise man was accustomed to enjoy the words of God; and by purity of heart and loftiness of vision to have the company of the good angels."
Objection 2. Further, the soul in the present state is impeded from the knowledge of separate substances by union with a corruptible body which "is a load upon the soul," as is written Wisdom 9:15. Wherefore the separate soul can see separate substances, as above explained (89, 2). But the body of the first man was not a load upon his soul; for the latter was not corruptible. Therefore he was able to see separate substances.
Objection 3. Further, one separate substance knows another separate substance, by knowing itself (De Causis xiii). But the soul of the first man knew itself. Therefore it knew separate substances.
On the contrary, The soul of Adam was of the same nature as ours. But our souls cannot now understand separate substances. 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; wherefore the first man is said to have been made into a "living soul"; that is, a soul giving life to the body--namely animal life. But he was endowed with integrity as to this life, in that the body was entirely subject to the soul, hindering it in no way, as we have said above (Article 1). Now it is clear from what has been already said (84, 7; 85, 1; 89, 1) that since the soul is adapted to perfect and govern the body, as regards animal life, it is fitting that it should have that mode of understanding which is by turning to phantasms. Wherefore this mode of understanding was becoming to the soul of the first man also.
Now, in virtue of this mode of understanding, there are three degrees of movement in the soul, as Dionysius says (Div. Nom. iv). The first is by the soul "passing from exterior things to concentrate its powers on itself"; the second is by the soul ascending "so as to be associated with the united superior powers," namely the angels; the third is when the soul is "led on" yet further "to the supreme good," that is, to God.
In virtue of the first movement of the soul from exterior things to itself, the soul's knowledge is perfected. This is because the intellectual operation of the soul has a natural order to external things, as we have said above (Question 87, Article 3): and so by the knowledge thereof, our intellectual operation can be known perfectly, as an act through its object. And through the intellectual operation itself, the human intellect can be known perfectly, as a power through its proper act. But in the second movement we do not find perfect knowledge. Because, since the angel does not understand by turning to phantasms, but by a far more excellent process, as we have said above (Question 55, Article 2); the above-mentioned mode of knowledge, by which the soul knows itself, is not sufficient to lead it to the knowledge of an angel. 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. And it was on account of this excellence of knowledge that Gregory says that "he enjoyed the company of the angelic spirits."
This makes clear the reply to the first objection.
Reply to Objection 2. That the soul of the first man fell short of the knowledge regarding separate substances, was not owing to the fact that the body was a load upon it; but to the fact that its connatural object fell short of the excellence of separate substances. We, in our present state, fall short on account of both these reasons.
Reply to Objection 3. The soul of the first man was not able to arrive at knowledge of separate substances by means of its self-knowledge, as we have shown above; for even each separate substance knows others in its own measure.
Source: Summa Theologica (New Advent)