The Levites are to camp around the Tabernacle of the Testimony, so that there will be no wrath unleashed on the community of Bnei-Yisrael. So the Levites are to maintain care of the Tabernacle of the Testimony.
Numbers 1:53

God placed the Levites as a spiritual covering/barrier over the people of Israel. He didn't put them between himself and the people because of any animosity he felt toward them, but because his presence, like fire or radiation, is dangerous.