If God would simply wipe out all sin, the result of the fall and the desire to sin in Mary, why not do that for all man kind and skip the whole cross thing?
He certainly could’ve, but He wanted to show how much He loved us. And He gave us a free will so that we could reject Him if we chose.
If you agree that God is the same yesterday, today, and tomorrow, then who He is never changes. All of God’s instructions to Moses (and Moses’ shining face after being in the presence of God), Isaiah’s attitude of humility and the angel having to touch his lips with the burning coal to purify him, all the incidents in the Old Testament such as when David brought the Ark of the Covenant back and a man reached out his hand to steady it on the cart and then was struck dead for touching it, makes you realize how holy God is. It doesn’t make sense that He would live and grow inside a woman who was not totally pure and holy. If a man could die merely from touching the Ark of the Covenant, there is no way that a woman could live and carry God in her womb if she were not totally pure and holy.