‘ And Joshua, the son of Nun, called the priests and said to them, “Take up the Ark of the covenant, and let seven priests bear seven trumpets of rams' horns before the Ark of YHWH.”
YHWH had given his instructions to Joshua, possibly through a dream, or possibly within the Tabernacle where Joshua, like Moses, was prone to go (Exodus 33:11) as the chosen of YHWH. Joshua now passed them on to the priests. Note the switch from ‘the Ark of the Covenant' to ‘the Ark of YHWH'. Now that it was going into battle the emphasis was on YHWH, the God of battle.