Why did God become human?
What is the meaning behind it?
The deeper level of the Christmas story is that God became man. This taking on of human form is called 'incarnation' by the church. Both in the Bible and by Christian philosophers much thought is applied into the meaning of this. There are several ideas that complement each other:
God makes himself vulnerable. If he stays 'safely' in heaven, he is unassailable, and no Herod the Great for example can do anything to him. Now he can be touched, he can even be executed. God shows here that he is never self-serving, and never does anything to anyone that he is not willing to go through himself.
God is going to 'experience' us. Before, God could only sympathize with people, but now he is going much further: 'He is able to empathize with our weaknesses because he has been tempted in every way, just as we are... so he is able to deal gently with those who are ignorant and are going astray.'
People can get to know God. Never was God closer to people than in Jesus. He becomes real, tangible, touchable. If someone is searching, they now have a sort of 'picture': the way Jesus is, so is God apparently.
Life becomes 'holy'. In Jesus' days, the idea was prevalent that the body was actually inferior and that truth was a dark place. But clearly God is not at all afraid to be 'stained' by it/ He has no problems with walking around on earth. God and man are able to be together. That must mean that it is possible for things to be well for all people in the future.
Humiliated people will be elevated. Often we blame poverty and the like on the people themselves, don't we? But here we see Jesus growing up in poverty, un an ignorant part of the world, without any status. If he did that, then every person living in poverty becomes 'suspect': who is to say they aren't also some kind of Jesus!
Evil is exposed. Peoples' true motives become clear by the way they respond to Jesus: 'This child is destined to cause the falling and rising of many in Israel... so that the thoughts of many hearts will be revealed.'