John Gill Commentary 1 Chronicles 16:37

"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;" — 1 Chronicles 16:37 (ASV)

So he left there, before the ark of the covenant of the Lord,
Asaph and his brethren
Whom he, that is, David, had appointed for the service of it:

to minister before the ark continually ;
in singing the praises of God:

as every day's work required ;
at the time of the morning and evening sacrifice, as Jarchi and Kimchi interpret it.