Ambrose of Milan — as excerpted in the Catena Aurea on Luke 3:23-38

“What could better agree than that the holy generation should commence from the Son of God, and be carried up even to the Son of God; and that he who was created should precede in a figure, in order that he who was born might follow in substance, so that he who was made after the image of God might go before, for whose sake the image of God was to descend. For Luke thought that the origin of Christ should be referred to God, because God is the true progenitor of Christ, or the Father according to the true birth, or the Author of the mystical gift according to baptism and regeneration, and therefore he did not from the first begin to describe His generation, but not till after he had unfolded His baptism, that both by nature and by grace, he might declare Him to be the Son of God. But what more evident sign of His divine generation than that when about to speak of it St. Luke introduces first the Father, saying, Thou art my beloved Son?”