Gen 17:19, Gen 21:2, Mt 1:2,16, Lk 3:23,34
God protected Abraham's wife. Because Christ will come as the descendant of Abraham's wife. (Gen 20:7, Gen 17:19)
Gen 20:7 Now therefore restore the man his wife; for he is a prophet, and he shall pray for thee, and thou shalt live: and if thou restore her not, know thou that thou shalt surely die, thou, and all that are thine.
Gen 17:19 And God said, Sarah thy wife shall bear thee a son indeed; and thou shalt call his name Isaac: and I will establish my covenant with him for an everlasting covenant, and with his seed after him.
Abraham had a son Isaac by Sarah. And Christ came as the descendant of Isaac. (Gen 21:2, Matthew 1:2,16, Luke 3:23,34)
Gen 21:2 For Sarah conceived, and bare Abraham a son in his old age, at the set time of which God had spoken to him.
Matthew 1:2 Abraham begat Isaac; and Isaac begat Jacob; and Jacob begat Judas and his brethren; 16 And Jacob begat Joseph the husband of Mary, of whom was born Jesus, who is called Christ.
Luke 3:23 And Jesus himself began to be about thirty years of age, being (as was supposed) the son of Joseph, which was the son of Heli, 34 Which was the son of Jacob, which was the son of Isaac, which was the son of Abraham, which was the son of Thara, which was the son of Nachor,