1) Christ is being contrasted with Adam, who with Eve wanted to be like God. Rather, he emptied himself.
2) The text is referring to the preexistent Christ, the prebirth Jesus, who emptied himself to become human; that is, vulnerable, even to the point of being executed.
3) Paul's first hearers would have been aware that the Roman emperor claimed to be "in the form of God" and regarded "equality with God as something to be exploited." They would have heard the claims that the emperor was divine, Lord, Son of God, Savior of the World, bringer of peace on earth. Paul is making the radical claim that Jesus Christ is the one who deserves the titles instead of Caesar.
Borg and Crossan say we don't have to choose between these three interpretations:
All make the same claim. What we see in Jesus--Christ crucified and raised as "Jesus Christ the Lord"--is the way, the path. This, Paul says in this text, is the mind that the followers of Jesus are to have. What we see in Jesus is the way, the path, of personal transformation. And it is the way, the path, of advocacy of a way of life very different from and in opposition to the normalcy of "this world." And it would cost Paul his life.