Heidelberg Catechism - Lord's Day 14

35. Q . What does it mean that he was conceived by the Holy Spirit and born of the virgin Mary”?
      A. That the eternal Son of God, who is and remains true and eternal God, took to himself, through the working of the Holy Spirit, from the flesh and blood of the virgin Mary, a truly human nature so that he might also become David’s true descendant, like his brothers and sisters in every way except for sin.

36. Q . How does the holy conception and birth of Christ benefit you?
      A. He is our mediator and, in God’s sight, he covers with his innocence and perfect holiness my sinfulness in which I was conceived.