'Duty' in the Bible

This is what you must do. One third of you priests and Levites who are on duty during the Sabbath will guard the doors.

No one must enter the Lord's temple except the priests and Levites who are on duty. They may enter because they are ceremonially pure. All the others should carry out their assigned service to the Lord.

The Levites and all the men of Judah did just as Jehoiada the priest ordered. Each of them took his men, those who were on duty during the Sabbath as well as those who were off duty on the Sabbath. Jehoiada the priest did not release his divisions from their duties.