The Levites could only undertake their duties (Numbers 3; Numbers 4) after the formal exchange of the Levites for the first-…

And after that the Levites shall go in ... — that is, into the court of the Tabernacle to keep watch there, and to assist the prie…

An offering must be presented for us before we can offer ourselves as an offering to God.

And after that shall the Levites go in
Not into the sanctuary, where only the priests entered, much le into the most…

Here we have directions for the solemn ordination of the Levites. All Israel must know that they did not take this honor to themselves, but were ca…