What's the difference between worship and slave?

Well worship is like worshiping God. Slave is someone who was sold to another person and is forced to do what the boss tells them and if they don't they can some times get a brutle punishment.

worship: reverent honor and homage paid to God or a sacred personage, or to any object regarded as sacred.

slave: person who is the property of and wholly subject to another; a bond servant.

You cannot be serious. You just can't be.

There is none. If you worship a god, you have eternal damnation (punishment) to fear, so in your mind, worship becomes mandatory to avoid said punishment. Also, psychologically speaking, it's almost impossible to stop believing, especially if you were raised into a religion. Faith becomes part of your subconscious and gives you little space for choice and actual freedom.