Why is it said that God’s two incarnations complete the significance of the incarnation?

Bible Verses for Reference:

“So Christ was once offered to bear the sins of many; and to them that look for him shall he appear the second time without sin to salvation” (Heb 9:28).

“In the beginning was the Word, and the Word was with God, and the Word was God” (Jhn 1:1).

Relevant Words of God: