Luke 1:35
And the angel answered and said to her [Mary], The Holy Spirit will come upon you, and the power of the Most High will ²overshadow you; therefore also the holy thing which is born will be called the Son of God.

    35² Such a conception of the Holy Spirit in the human virgin, accomplished with the divine and human essences, constituted a mingling of the divine nature with the human nature, which produced a God-man, One who is both the complete God and the perfect man, possessing the divine nature and the human nature distinctly, without a third nature being produced. This is the most wonderful and most excellent person of Jesus.