Jesus assumed the form of a slave even though he was equal to God
Dr. Roberto Miranda(Audio: Spanish)
The idea that we are servants, we are slaves, we are totally dependent on the Will of God, is part of the whole context of the Gospel. And that is why the apostle Paul always considered himself precisely as a servant and as a slave of the Lord Jesus Christ. In almost all of his epistles the apostle Paul identified himself as Paul the servant, doulos of Jesus Christ.
For example in Philippians chapter 1 verse 1, Paul introduces himself this way: "Paul and Timothy, servants, doulos" right? which is the Greek word for slave, "doulos of Jesus Christ, to all the saints in Christ Jesus who are in Philippi, etc. Paul at all times considered himself a mere slave of the Lord because he wanted to emphasize that idea that his life was Totally at the Father's disposal for whatever God wanted to do with him, he saw himself as a mere instrument.