John Gill Commentary 1 Chronicles 15:27

"And David was clothed with a robe of fine linen, and all the Levites that bare the ark, and the singers, and Chenaniah the master of the song [with] the singers: and David had upon him an ephod of linen." — 1 Chronicles 15:27 (ASV)

And David was clothed with a robe of fine linen
For though a king, he, being among the singers, was clothed as they; for so it follows:

and all the Levites that bore the ark, and the singers, and Chenaniah
the master of the song ;
or of those that bore the burden, the ark, as the Targum:

with the singers ;
all were clothed in robes of fine linen:

David also had upon him an ephod of linen ;
which he had besides his linen robe, and was over it; and being a shorter and tighter garment, it bound the other closer to him; though some think this is explanative of the former, and designs the same, and is what others, besides priests, were, on occasion, allowed to wear, see (1 Samuel 2:18) .