Albert Barnes Commentary 1 Chronicles 15:2

"Then David said, None ought to carry the ark of God but the Levites: for them hath Jehovah chosen to carry the ark of God, and to minister unto him for ever." — 1 Chronicles 15:2 (ASV)

No one should carry the ark of God except the Levites—Compare the marginal references. We can easily understand that David, after the “breach upon Uzza” (1 Chronicles 13:11), had carefully considered all the legal requirements for moving the ark and was anxious that they should be strictly observed (Compare to 1 Chronicles 15:13).