I don't believe he says anything about it. The virgin birth is spoken of in Matthew 1:23 and Luke 1:27.

In the Greek Scriptures, or New Testament, we find but some fifty references to Mary, the mother of Jesus, but 1,750 references to Jesus Christ the Son, and 1,850 to God the Father. In fact, there is but a single reference to her in all the Acts of the apostles and she is ignored entirely in all the letters by Paul, James, Peter, Jude and John What was the impact of Mary giving birth to Gods’ perfect Son? In Romans chapters 5 and 6, Paul gives a fine explanation of it. At Romans 5:12 he explains our inherited sin and death. He goes on to show how the effect of just one sin by perfect Adam and the forfeiture of life for his offspring could be balanced by another perfect human life. That proved to be the life of the “man Jesus Christ.” (Verses 15-21; see also 1 Timothy 2:5, 6.) Why could Jesus provide this ransom? Because he was the Son of God, Jesus was “loyal, guileless, undefiled, separated from the sinners.” (Hebrews 7:26; Luke 1:32, 33) We need not attempt to explain the details of the genetics of Jesus’ birth. The angel Gabriel assured Jesus’ mother, Mary, and us, that nothing is impossible with God. (Luke 1:37) So Jesus, although born out of a female descendant of Adam, was the Son of God—actually a perfect man. His blood, or life, was worth far more than the blood of countless animals that had been sacrificed by the Aaronic priests of Israel at the temple in Jerusalem. He was “the Lamb of God that takes away the sins of the world. For that, we can all be very thankful.