Isaiah 9:6 begins with these words-

For to us a child is born, To us a son is given;

Jesus was born fully human and still remained fully God.  But why?

The child was born for us.  The Son was given for us – promising life as the gift of God.

And this is the testimony, that God gave us eternal life, and this life is in his Son. Whoever has the Son has life; whoever does not have the Son of God does not have life. (1 John 5:11-12)

And on a Christmas day nearly five hundred years ago, Martin Luther preached these words-

For whom was he conceived and born? For whom did he suffer and die? For us, for us, for us! Always add us! That is why the church fathers rightly put the word: “And in Jesus Christ, our Lord.” into the creed. We should relate this word to every sentence: He was conceived for us and born for us, suffered for us and raised for us, ascended for us and sitting at the right [hand of God] for us.

Consider that simple phrase today.  For us.