'Duty' in the Bible

I said to them, “Do not open the gates of Jerusalem until the sun is hot, and let the doors be shut and securely fastened while the guards are on duty. Station the citizens of Jerusalem as guards, some at their posts and some at their homes.”

They performed the duty of their God, and the duty of the purification, and [so did] the singers and the porters, according to the commandment of David, and of Solomon his son.