'Duty' in the Bible

When his division was on duty and he was serving as priest before God,

In the same way, when you have done all that you were commanded, you should say, ‘We are good-for-nothing slaves; we’ve only done our duty.’”

Therefore, brothers, select from among you seven men of good reputation, full of the Spirit and wisdom, whom we can appoint to this duty.

A husband should fulfill his marital responsibility to his wife, and likewise a wife to her husband.