It's as easy as A B C
1. Jesus has two natures — He is God and man.
2. Each nature is full and complete — He is fully God and fully man.
3. Each nature remains distinct.
Jesus... fully God, Fully Man... The God Man
For to us a Child is born, to us a Son is given; and the government shall be upon His shoulder, and His name shall be called Wonderful Counselor, Mighty God, Everlasting Father [of Eternity], Prince of Peace. Of the increase of His government and of peace there shall be no end, upon the throne of David and over his kingdom, to establish it and to uphold it with justice and with righteousness from the [latter] time forth, even forevermore. The zeal of the Lord of hosts will perform this.
Isaiah 9:6–7
A. The first truth we need to understand is that Jesus is one Person who has two natures: a divine nature and a human nature. In other words, Jesus is both God and man.
B. It should be obvious that if Jesus is God, then he has always been God. There was never a time when he became God, for God is eternal. But Jesus has not always been man. The fantastic miracle is that this eternal God became man through the incarnation approximately 2,000 years ago. That’s what the Incarnation was: God the Son becoming man. And that is the great event we celebrate at Christmas.
C. For most people it is obvious that Jesus will be God forever. But for some reason it escapes a lot of us that Jesus will also be man forever.