Luke 1:35

And the angel answered and said unto her, The Holy Spirit shall come upon thee, and the power of the Most High shall overshadow thee: wherefore also the holy thing which is begotten shall be called the Son of God.

This record of what the archangel Gabriel said to the virgin mother of our Lord is unimpeachable. With Spence we agree that Luke's narrative here derives from the lips of Mary herself; and, as for the meaning of what was promised in this announcement, the words of Bishop Pearson on the Creed are appropriate:

The Word was conceived in the womb of a woman, not after the manner of men, but by the singular, powerful, invisible, immediate operation of the Holy Spirit, whereby a virgin, beyond the law of nature, was enabled to conceive; and that which was conceived in her was originally and completely sanctified.[28]

The power of the Most High shall overshadow thee ... Ash has this beautiful word on the "overshadowing" of Mary:

"Overshadow" recalls the cloud over the tabernacle during the wilderness wandering. The word is used in all the synoptic Gospels of the cloud that came at the transfiguration. The only other New Testament usage is in Acts 5:15. The term is always used of divine power. The concept is reminiscent of the Spirit hovering over the waters in Genesis 1:2. Here the Spirit would be active in a new "creation" of God.[29]

This whole paragraph regarding the annunciation is fantastically beyond the power of any mere human being to have invented it. Like many other passages in the Bible, this lies utterly beyond the perimeter of anything that the natural man might have imagined.

[28] H. D. M. Spence, op. cit., p. 8.

[29] Anthony Lee Ash, op. cit., p. 39.