דברי הימים א, פרק ט״ו, פסוק י״א

In preparation for relocating the Ark of the Covenant, King David carefully organizes the leadership, establishing a clear division of responsibilities between the priests and the Levites. He begins by addressing Zadok and Abiathar, the chief priests who stand at the head of this operation [ביאור שטיינזלץ].

David approaches the priests first because they have an essential, preliminary duty to fulfill. Before the Levites can safely carry the Ark, the priests must step forward to conceal it. They are tasked with covering the sacred object with the dividing curtain, a protective leather covering, and a cloth of pure blue [מלבי״ם].

Only after this crucial preparation is complete does David call upon the Levites. He summons Uriel, Asaiah, Joel, Shemaiah, Eliel, and Amminadab, the heads of the Levite families. These leaders are entrusted with the actual physical labor of lifting and transporting the Ark once the priests have properly covered it [ביאור שטיינזלץ].