'Duty' in the Bible

Now while he was doing priestly duty before God in the prescribed course of his class,

"Why is it that you have been searching for me?" He replied; "did you not know that it is my duty to be engaged upon my Father's business?"

and forgive us our sins, for we ourselves also forgive every one who fails in his duty to us; and bring us not into temptation.'"

Or those eighteen on whom the tower at Siloam fell, do you suppose they had failed in their duty more than all the rest of the people who live in Jerusalem?

So you also, when you have obeyed all the orders given you, must say, "'There is no merit in our service: what we have done is only what we were in duty bound to do.'"