Okay—following your logic : if he did, then why did he have to come and die? If God required someone sinless to pay the price for us all, Mary could have been that person, right?? She could have died for our sins.
Let me ask you: why couldn’t God preserve himself from sin by being born of Mary—a sinful human like us—is he unable to do that? Is not God truly almighty and able to do whatever he pleases? If so, why couldn’t he use Mary, warts and all??
Hoss
The bridge works both ways.
Christ is fully God and fully Man. When you are drowning, you need someone with their feet firmly on the other bank. You need God.
Christ before the incarnation was fully God, but he needed to become Fully Man, the same as Adam. Hence the miracle of the incarnation, where he became exactly this, the new Adam.
This is why it couldn’t be Mary, because Mary is not God.
“Why couldn’t God preserve himself from sin by being born of Mary.”
He could have taken on the likeness of Man, but it wouldn’t be the same thing. He had to take the flesh and be reformed of the flesh while he is in his mother’s womb. This means he no longer has control over the process once it’s started.