There is a big difference between a slave and a volunteer. A slave is bound to his master. He must do what he says. He must do it when he says, how he says, and without delay. There is no choice in the matter.
A volunteer, on the other hand, plays by different rules. Like the slave, he too will do works of service. However, unlike the slave, he gives his service when it is convenient to him. If the weather is bad or if he’s busy doing something else or if he plain doesn’t like something, he can always back out.
When it comes to serving Jesus, many people come to him, thinking that being a volunteer in the church is enough. They think that giving a few hours here and there upon their convenience is good enough for Jesus. It isn’t. We come to Jesus as slaves. Paul considered himself a slave, “Paul, a slave of Christ Jesus” (Romans 1:1). All who follow Christ are slaves of righteousness. “Thanks be to God that though you were slaves of sin, you became obedient from the heart to that form of teaching to which you were committed, and having been freed from sin, you became slaves of righteousness” (Romans 6:17-18).