Priests Is Not a Vocation, Right?

In 147, we read the Levites were not listed along with them by their ancestral tribe and there's explanation given. And then in verse 50, the Lord tells Moses, a point the Levites over the tabernacle of the testimony and all its furnishings. So it seems that you have this almost like this buffer zone tribe that is encamped around the tabernacles. They do things like ensure the preservation of men who are vital to the purposes of God.