1 Chronicles 23:13
The sons of Amram; Aaron and Moses: and Aaron was separated, that he should sanctify the most holy things, he and his sons for ever, to burn incense before the Lord, to minister unto him, and to bless in his name for ever. (1 Chronicles 23:13)
Most holy things.
The sons of Aaron were engaged in the most sacred work of the sanctuary, namely, the burning of incense and other ministrations before Jehovah.
Aaron was separated.
 The sons of Aaron, the priests in Israel, are not included in the present list, but are enumerated separately in ch. 24:1-19.