1 Chronicles 24:19

This was the ordering of them in their service, to come into the house of LORD according to the ordinance [given] to them by Aaron their father, as LORD, the God of Israel, had commanded him.

1 Chronicles 9:25

And their brothers, in their villages, were to come in every seven days from time to time to be with them;

1 Chronicles 24:1

And the divisions of the sons of Aaron [were these]. The sons of Aaron: Nadab and Abihu, Eleazar and Ithamar.

2 Chronicles 23:4

This is the thing that ye shall do: A third part of you who come in on the Sabbath, of the priests and of the Levites, shall be porters of the thresholds,

2 Chronicles 23:8

So the Levites and all Judah did according to all that Jehoiada the priest commanded. And they took every man his men, those who were to come in on the Sabbath, with those who were to go out on the Sabbath. For Jehoiada the priest

1 Corinthians 14:40

Let all things be done decently and in order.

Hebrews 7:11

If indeed therefore perfection was through the Levitical priesthood (for under it the people had received the law), what further need is there for another priest to arise according to the order of Melchizedek, and not be designated

Treasury of Scripture Knowledge

Summary

These were the orderings of them in their service to come into the house of the LORD, according to their manner, under Aaron their father, as the LORD God of Israel had commanded him.

Bible References

The orderings

1 Chronicles 9:25
And their brothers, in their villages, were to come in every seven days from time to time to be with them;
2 Chronicles 23:4
This is the thing that ye shall do: A third part of you who come in on the Sabbath, of the priests and of the Levites, shall be porters of the thresholds,
1 Corinthians 14:40
Let all things be done decently and in order.

Under aaron

1 Chronicles 24:1
And the divisions of the sons of Aaron [were these]. The sons of Aaron: Nadab and Abihu, Eleazar and Ithamar.
Hebrews 7:11
If indeed therefore perfection was through the Levitical priesthood (for under it the people had received the law), what further need is there for another priest to arise according to the order of Melchizedek, and not be designated