'Duty' in the Bible

Now it happened while Zacharias was serving as priest before God in the appointed order of his priestly division,

And He answered, “Why did you have to look for Me? Did you not know that I had to be in My Father’s house?”

So you too, when you have done everything that was assigned and commanded you, say, ‘We are unworthy servants [undeserving of praise or a reward, for we have not gone beyond our obligation]; we have merely done what we ought to do.’”