Matthew Henry on 1 Chronicles 16:37-43

The worship of God ought to be the work of every day. David put it into order. At Jerusalem, where the ark was, Asaph and his brethren were to minister before the ark continually, with songs of praise. No sacrifices were offered there, nor incense burnt, because the altars were not there; but David's prayers were directed as incense, and the lifting up of his hands as the evening sacrifice. So early did spiritual worship take place of ceremonial. Yet the ceremonial worship, being of Divine institution, must by no means be omitted; therefore at Gibeon, at the altars, the priests attended; for their work was to sacrifice and burn incense; and that they did continually, morning and evening, according to the law of Moses. As the ceremonies were types of the mediation of Christ, the observance of them was of great consequence. The attendance of his appointed ministers is right in itself, and encourages the people.