In a nutshell, here's the Christmas story: Jesus came to pay a debt He didn't owe, because you and I owed a debt we couldn't pay.
Before Jesus was born Joseph was instructed, "She will give birth to a son, and you are to give him the name Jesus, because he will save his people from their sins" (Matthew 1:21).
So why would God do that? "Because of his great love for us, God, who is rich in mercy, made us alive with Christ even when we were dead in transgressions–it is by grace you have been saved" (Ephesians 2:4-5).
The towering motive behind Christmas is that God loves each one of us very much.