6 What then, some man will say, is it not written, The little ones' Angels do always behold the face of My Father which is in heaven? Yes, but the Angels see God not as He is, but as far as they themselves are capable. For it is Jesus Himself who says, Not that any man has seen the Father, save He which is of God, He has seen the Father. The Angels therefore behold as much as they can bear, and Archangels as much as they are able; and Thrones and Dominions more than the former, but yet less than His worthiness: for with the Son the Holy Ghost alone can rightly behold Him: for He searches all things, and knows even the deep things of God: as indeed the Only-begotten Son also, with the Holy Ghost, knows the Father fully: For neither, says He, knows any man the Father, save the Son, and he to whom the Son will reveal Him. For He fully beholds, and, according as each can bear, reveals God through the Spirit: since the Only-begotten Son together with the Holy Ghost is a partaker of the Father's Godhead.
He, who was begotten knows Him who begot; and He Who begot knows Him who is begotten. Since Angels then are ignorant (for to each according to his own capacity does the Only-begotten reveal Him through the Holy Ghost, as we have said), let no man be ashamed to confess his ignorance. I am speaking now, as all do on occasion: but how we speak, we cannot tell: how then can I declare Him who has given us speech? I who have a soul, and cannot tell its distinctive properties, how shall I be able to describe its Giver?
Source: Catechetical Lectures (New Advent)