'Slave' in the Bible

Were you called as a slave? Do not worry about it. But if indeed you are able to be free, make the most of the opportunity.

For the one who was called in the Lord as a slave is the Lord's freedman. In the same way, the one who was called as a free person is Christ's slave.

For since I am free from all I can make myself a slave to all, in order to gain even more people.

Instead I subdue my body and make it my slave, so that after preaching to others I myself will not be disqualified.