Charles Ellicott Commentary Numbers 8:5

"And Jehovah spake unto Moses, saying," — Numbers 8:5 (ASV)

And the Lord spoke to Moses. — As Moses had already officiated in the consecration of the priests (Leviticus 8:0), so now, notwithstanding the fact that Aaron and his sons were already consecrated, he is commanded to officiate at the cleansing of the Levites.