'Duty' in the Bible

And Judah said unto Onan, Go in unto thy brother's wife, and perform the duty of a husband's brother unto her, and raise up seed to thy brother.

If he take him another wife ; her food, her raiment, and her duty of marriage, shall he not diminish.

If brethren dwell together, and one of them die, and have no son, the wife of the dead shall not be married without unto a stranger: her husband's brother shall go in unto her, and take her to him to wife, and perform the duty of a husband's brother unto her.

And if the man like not to take his brother's wife, then his brother's wife shall go up to the gate unto the elders, and say, My husband's brother refuseth to raise up unto his brother a name in Israel; he will not perform the duty of a husband's brother unto me.

even as the duty of every day required, offering according to the commandment of Moses, on the sabbaths, and on the new moons, and on the set feasts, three times in the year, even in the feast of unleavened bread, and in the feast of weeks, and in the feast of tabernacles.

And he appointed, according to the ordinance of David his father, the courses of the priests to their service, and the Levites to their offices, to praise, and to minister before the priests, as the duty of every day required; the doorkeepers also by their courses at every gate: for so had David the man of God commanded.

besides them that were reckoned by genealogy of males, from three years old and upward, even every one that entered into the house of Jehovah, as the duty of every day required, for their service in their offices according to their courses;

And they kept the feast of tabernacles, as it is written, and offered the daily burnt-offerings by number, according to the ordinance, as the duty of every day required;

This is the end of the matter; all hath been heard: fear God, and keep his commandments; for this is the whole duty of man.