19 This was their appointed order of ministering when they entered the temple of the LORD, according to the regulations prescribed for them by their ancestor Aaron, as the LORD, the God of Israel, had commanded him.

Read 1 Chronicles 24:19 Using Other Translations

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.
These had as their appointed duty in their service to come into the house of the LORD according to the procedure established for them by Aaron their father, as the LORD God of Israel had commanded him.
Each group carried out its appointed duties in the house of the LORD according to the procedures established by their ancestor Aaron in obedience to the commands of the LORD, the God of Israel.