St. Leo the Great explains the importance of the genealogies of Jesus from the gospels of Matthew and Luke in the Office of Readings for December 17. God could have appeared as he did in the time of the patriarchs, in the guise of strangers who appeared to Abraham, in the mysterious figure who wrestled with Jacob. Instead, God chose to send his Son to be born in time and take on himself a human nature like ours.

“The divine nature and the nature of a servant were to be united in one person so that the Creator of time might be born in time, and he through whom all things were made might be brought forth in their midst.

  For unless the new man, by being made in the likeness of sinful flesh, had taken on himself the nature of our first parents, unless he had stooped to be one in substance with his mother while sharing the Father’s substance and, being alone free from sin, united our nature to his, the whole human race would still be held captive under the dominion of Satan. The Conqueror’s victory would have profited us nothing if the battle had been fought outside our human condition.

But through this wonderful blending the mystery of new birth shone upon us, so that through the same Spirit by whom Christ was conceived and brought forth we too might be born again in a spiritual birth; and in consequence the evangelist declares the faithful to have been born not of blood, nor of the desire of the flesh, nor of the will of man, but of God.“

He dwelt among us. He did not engage us “outside our human condition.”