19 But lest you should think that He is in a like sense Father of the Son and of the creatures, Christ drew a distinction in what follows. For He said not, “I ascend to our Father,” lest the creatures should be made fellows of the Only-begotten; but He said, My Father and your Father; in one way Mine, by nature; in another yours, by adoption. And again, to my God and your God, in one way Mine, as His true and Only-begotten Son, and in another way yours, as His workmanship. The Son of God then is Very God, ineffably begotten before all ages (for I say the same things often to you, that it may be graven upon your mind). This also believe, that God has a Son: but about the manner be not curious, for by searching you will not find. Exalt not yourself, lest you fall: think upon those things only which have been commanded you. Tell me first what He is who begot, and then learn that which He begot; but if you can not conceive the nature of Him who has begotten, search not curiously into the manner of that which is begotten.
Source: Catechetical Lectures (New Advent)