John Gill Commentary 1 Chronicles 6:49

"But Aaron and his sons offered upon the altar of burnt-offering, and upon the altar of incense, for all the work of the most holy place, and to make atonement for Israel, according to all that Moses the servant of God had commanded." — 1 Chronicles 6:49 (ASV)

Ver. 49-53. But Aaron and his sons Those that descended from him, though of the same tribe of Levi were all priests: and they offered upon the altar of burnt offerings; the daily sacrifice, and all the offerings of the people brought to them: and on the altar of incense; they burnt incense night and morning: and were appointed for all the work of the place most holy; such as were high priests of the line of Eleazar, whose work it was to go into the most holy place once a year: to make atonement for all Israel, according to all that Moses the servant of God commanded; in (Leviticus 16:1) which see; and on mention of this, a list of the high priests from Aaron, in the line of Eleazar, is given, to the times of Solomon, in the four following verses, just in the same order as in (1 Chronicles 6:4–8) .