It is a complex concept, and quite difficult to grasp, but the scriptures do show it to be true. I don't want to quote a bunch of scriptures here to prove it, but I can do that upon request. In this way he was fully a man. Yet he was and is the Son of God from eternity past. He became man also when he was born to Mary, and as a man he lived and walked the earth, and died, yet all the while he was also God.
Salvation is by faith, plus nothing.
No man is saved by works. Believe the Gospel and you are saved. Simple as that. You are saved by God's Grace alone. We can't possibly earn salvation, no one can be that good as to earn it.