It's important to remember that the divine Person we know as Jesus did not stop being God so he could become a man instead. What he did was become a man also, so that he is now not only God, but the God-Man.
That is to say, as a divine Person, he now has two natures: (1) his divine nature from eternity, and (2) his newly aquired human nature (i.e., body and soul), which he assumed from Mary.
He never became God. Nor can he ever cease being God. But he did begin to be man -- just 2000 years ago. And he will henceforth always be a man.
#Christmas -- which I'm already looking forward to -- is not a party for us to shout, "Happy birthday, Jesus! 🎂"
It's a joyful celebration of this mindboggling mystery of the Incarnation, the central mystery of our Faith.