It is not that much of a mystery. Abraham was promised that through his seed (DNA) all the Nations would be blessed. Therefore Jesus had to be a blood descendant of Abraham.
2+2=4
If Jesus were not a blood descendant of Abraham, then he was not the Messiah.
What good are prophecies if they are not fulfilled?
Tha's what happens when one reads the Bible literally, the Protestant way. Abraham's children did not come from Abraham's seed, they came from his seed and his wife's seed seed.
It's not 2+2=4, it's 1/2+1/2 = 1
The way some Protestants on this forum imagine Christ, he is indeed a demigod. But, then, once one takes the wrong exist one won't get back on track unless one makes a u-turn.