1 Chronicles 24:19

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

1 Chronicles 9:25

And their brethren, who were in their villages, came every seven days in their set times with them.

1 Chronicles 24:1

The sons of Aaron also had their courses. The sons of Aaron: Nadab, Abihu, Eleazar, and Ithamar.

2 Chronicles 23:4

This is the thing that ye must do: A third part of you, those who enter on the sabbath, shall be porters at the doors with the priests and the Levites;

2 Chronicles 23:8

So the Levites and all Judah did according to all the things that Jehoiada, the priest, had commanded, and each one took his men, those that were to come in on the sabbath with those that were to go out on the sabbath, for Jehoiada the priest did not dismiss the courses.

1 Corinthians 14:40

But let all things be done decently and in order.

Hebrews 7:11

If therefore perfection were by the Levitical priesthood (for under it the people received the law), what further need was there that another priest should rise after the order of Melchisedec and not be called after the order of Aaron?

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 brethren, who were in their villages, came every seven days in their set times with them.
2 Chronicles 23:4
This is the thing that ye must do: A third part of you, those who enter on the sabbath, shall be porters at the doors with the priests and the Levites;
1 Corinthians 14:40
But let all things be done decently and in order.

Under aaron

1 Chronicles 24:1
The sons of Aaron also had their courses. The sons of Aaron: Nadab, Abihu, Eleazar, and Ithamar.
Hebrews 7:11
If therefore perfection were by the Levitical priesthood (for under it the people received the law), what further need was there that another priest should rise after the order of Melchisedec and not be called after the order of Aaron?