'Ministering' in the Bible

As for us, Jehovah is our God, and we have not forsaken Him, and priests are ministering to Jehovah, sons of Aaron and the Levites, in the work,

And none doth enter the house of Jehovah except the priests, and those ministering of the Levites (they go in for they are holy), and all the people keep the watch of Jehovah:

My sons, be not now at rest, for on you hath Jehovah fixed to stand before Him, to serve Him, and to be to Him ministering and making perfume.'