Matthew Henry Commentary 1 Chronicles 16:37-43

"So he left there, before the ark of the covenant of Jehovah, Asaph and his brethren, to minister before the ark continually, as every day`s work required; and Obed-edom with their brethren, threescore and eight; Obed-edom also the son of Jeduthun and Hosah to be doorkeepers; and Zadok the priest, and his brethren the priests, before the tabernacle of Jehovah in the high place that was at Gibeon, to offer burnt-offerings unto Jehovah upon the altar of burnt-offering continually morning and evening, even according to all that is written in the law of Jehovah, which he commanded unto Israel; and with them Heman and Jeduthun, and the rest that were chosen, who were mentioned by name, to give thanks to Jehovah, because his lovingkindness [endureth] for ever; and with them Heman and Jeduthun [with] trumpets and cymbals for those that should sound aloud, and [with] instruments for the songs of God; and the sons of Jeduthun to be at the gate. And all the people departed every man to his house: and David returned to bless his house." — 1 Chronicles 16:37-43 (ASV)

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 brothers were to minister before the ark continually, with songs of praise. No sacrifices were offered there, nor was incense burned, 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 begin to fulfill the role of ceremonial worship.

Yet ceremonial worship, being of Divine institution, was by no means to be omitted. Therefore, at Gibeon, at the altars, the priests attended, for their work was to sacrifice and burn incense; and this they did continually, morning and evening, according to the law of Moses.

Since the ceremonies were types of the mediation of Christ, their observance was of great consequence. The attendance of his appointed ministers is right in itself and encourages the people.