The apostle John explains that before Jesus was born on earth he lived in the spirit realm as the firstborn Son of God and was called the Word. In due time “the Word became flesh and resided among us.” (John 1:1-14) Or, as expressed elsewhere in the Bible: “God sent forth his Son, who came to be out of a woman.” (Galatians 4:4) Jesus himself acknowledged that “on coming into the world: ‘[God] who wanted no [animal] sacrifice or oblation, prepared a body for me.’”—Hebrews 10:5, Jerusalem Bible.
There were strong reasons for Jesus’ becoming a human, “coming into the world” of mankind. High on the list was the redemption of the human family from slavery to sin, imperfection and death. The apostle Paul explained: “Through one man sin entered into the world and death through sin, and thus death spread to all men because they had all sinned.” (Romans 5:12) As to how Almighty God would cope with that situation, Paul says: “There is one God, and one mediator between God and men, a man, Christ Jesus, who gave himself a corresponding ransom for all.”—1 Timothy 2:5, 6; compare 1 Corinthians 15:21, 22.
Yes, death came to all humans through the rebellion of our forefather Adam, and justice required the life of another perfect man, not more, not less, to provide the ransom that would buy back the possibility of everlasting life for us. No imperfect human could possibly provide that. (Psalm 49:6, 7) Someone would have to step down from the heavenly realm. Appropriately, the one to do this was the firstborn Son of God. He had to become a perfect man and yet not lose his continuity of life. His life-force was not to be extinguished but would be transferred to the ovum of the virgin girl, Mary. She, ‘overshadowed by the protective power of the Most High,’ could produce a perfect body for the babe Jesus.—Luke 1:35.
This explains also why the life-force could not come through an imperfect human male in the normal way. An imperfect Jesus could not have become the ransom. Nor could he have become such as an incarnation or God/man.