Philippians 2:7 (ESV)

7 but emptied himself, by taking the form of a servant, being born in the likeness of men.

But Christ has emptied himself. He has emptied himself of being in the form of God. This does not mean that he divested himself of his being God. That is impossible, for God cannot cease to be God. He took the form of a slave; he became equal to men. This formulation shows that it is not primarily about the fact that Jesus became man, but about the self-humiliation of Jesus on earth. See also the context of the song, especially Philippians 2:3 and Philippians 2:5.