'Obligation' in the Bible

Now to someone who works, wages are not considered a gift but an obligation.

Consequently, brothers, we are not with respect to human nature, that is under an obligation to live according to human nature.

A husband should fulfill his obligation to his wife, and a wife should do the same for her husband.

But if the unbelieving partner leaves, let him go. In such cases the brother or sister is not under obligation. God has called you to live in peace.

For if I preach the gospel, I have nothing to boast about, for this obligation has been entrusted to me. How terrible it would be for me if I didn't preach the gospel!

For if I preach voluntarily, I get a reward, but if I am unwilling to do it, I am still entrusted with that obligation.