Jesus had to be 100% man and 100% God in order to redeem humanity. If He were only man and not God than he would be no different than other religious leaders. He would not have any power to redeem mankind as he himself would be in the same boat. He would be like a prisoner locked in one cell trying to set another prisoner free who is in another cell. Only those who are free can set others free.
Jesus, being 100% man, takes the title "Son of Man".
Simultaneously , Jesus who is 100% God, takes the title "Son of God".
On the other hand, if Jesus were 100% God and not man, then Jesus would not be a good substitutionary sacrifice. In other words, He died in our place, He took our sin. How can he identify with man in a practical and real sense without being man? And how can we identify with Him in a practical and real way if He were not human?
There are only two ways Jesus can be the Son of Man and the Son of God. Either God comes as a woman, and uses the seed of man. Or God comes as Father, and uses the womb of a woman.
Some people have the misconception that we are trying to say that God had sex with Mary. Absolutely not! This is evil.
God, the Father came by the Holy Spirit. The Holy Spirit, by supernatural means (NOT natural) conceived Jesus within Mary.
Also, God choose to initiate His redemption through a woman as a counteraction of Satan's initiation of sin into the world through a woman.
Satan chose a woman to initiate sin into the world. God has to choose a woman to undo what Satan done.
Likewise, sin came into the world by taking the "fruit" off the tree. God, counteracted that, by putting the fruit (Jesus) back on the tree (cross).