There are several basic points in being a slave:
1. The master creates value, but the slave can't do anything at all.
2, the master gives all happiness, and the slave can only bring a burden to the master.
3, the master is eternal, and the slave is from generation to generation.
4, the master is king, and the slave loves the master
If Christians want to repay God's grace, they should not only be slaves of God in the world, but also continue to be slaves of the master forever when they come to the kingdom of heaven.