1. But it cannot be said that the soul of itself knows concerning itself what it essentially is. For a cognitive faculty comes to be actually cognisant by there being in it the object which is known. If the object is in it potentially, it knows potentially: if the object is in it actually, it is actually cognisant: if in an intermediate way, it is habitually cognisant. But the soul is always present to itself actually, and never potentially or habitually only. If then the soul of itself knows itself by its essence, it must ever have an intellectual view of itself, what it essentially is, which clearly is not the case.
2 and 3. If the soul of itself knows itself in its essence, every man, having a soul, knows the essence of the soul: which clearly is not the case, for many men have thought the soul to be this or that body, and some have taken it for a number or harmony.
So then, by knowing itself, the soul is led to know concerning separately subsistent intelligences the fact of their existence, but not what they are essentially, which would mean understanding their substances. For whereas we know, either by demonstration or by faith, concerning these pure spirits that they are intelligent subsistent beings, in neither way could we gather this knowledge but for the fact that our soul knows from itself the meaning of intelligent being. Hence we must use our knowledge of the intelligence of our own soul as a starting-point for all that we can know of separately subsistent intelligences. But even granting that by speculative sciences we could arrive at a knowledge of the essence of our own soul, it does not follow that we could thereby arrive at a knowledge of all that is knowable about pure spirits; for our intelligence falls far short of the intelligence of a pure spirit. A knowledge of the essence of our own soul might lead to a knowledge of some remote higher genus of pure spirits: but that would not be an understanding of their substances.
3.41 - 45 : [That we cannot find happiness in this life by sharing an angel's natural knowledge of God]
3.47 : That we cannot in this Life see God as He essentially is