'Ministering' in the Bible

Now according to the ordinance of his father David, he appointed the divisions of the priests for their service, and the Levites for their duties of praise and ministering before the priests according to the daily rule, and the gatekeepers by their divisions at every gate; for David the man of God had so commanded.

But as for us, the Lord is our God, and we have not forsaken Him; and the sons of Aaron are ministering to the Lord as priests, and the Levites attend to their work.

But let no one enter the house of the Lord except the priests and the ministering Levites; they may enter, for they are holy. And let all the people keep the charge of the Lord.