he emptied himself: He gave up his divine privileges and chose to live as a human. The rest of verses 7–8 explains this ultimate act of godly self-giving love (compare 2 Corinthians 8:9).
taking the form of a servant: Paul might have been thinking of Isaiah 52:13–53:12.
being made in human likeness: Jesus became truly human while still being God (see John 1:14; 1 Timothy 3:16).