John Gill Commentary 1 Chronicles 15:12

"and said unto them, Ye are the heads of the fathers` [houses] of the Levites: sanctify yourselves, both ye and your brethren, that ye may bring up the ark of Jehovah, the God of Israel, unto [the place] that I have prepared for it." — 1 Chronicles 15:12 (ASV)

And he said to them, you are the chief of the fathers of the Levites Of the families of the Levites, heads of their fathers' houses:

sanctify yourselves, both you and your brethren ; respectively under each, whose numbers are before given, by washing their bodies and clothes, and abstaining from their wives:

that you may bring up the ark of the Lord God of Israel to the place that I have prepared for it ; (2 Samuel 6:17) .