The 34th mitzvah is that we are commanded that the kohanim shall carry the ark on their shoulders whenever it is moved from one place to another.

The source of this mitzvah is G‑d's statement1 (exalted be He), "[He did not give any wagons to the descendants of Kehos] since they had responsibility for the most sacred articles, that they had to carry on their shoulders."

And even though the commandment was said at that time to the Levites,2 this was only because Aaron was the first kohen, and therefore the number of kohanim at that time was very small. For future generations, however, this mitzvah in incum­bent on the kohanim. They are the ones who are required to carry it, as explained in the Book of Joshua3 and the Book of Samuel.4

When Dovid commanded the transportation of the ark the second time, it is written in Chronicles,5 "The sons of the Levites6 carried the ark of G‑d on their shoulders with poles, as Moshe commanded in the name of G‑d."7 Similarly, when the division of the kohanim into 24 watches is mentioned in Chronicles,8 it is written thereafter, "These have been ap­pointed to serve in the House of G‑d as commanded to their father Aaron, as commanded by G‑d, the G‑d of Israel." Our Sages explained that this hints to the service of the kohanim of carrying the ark on their shoulders — this is what was "commanded by G‑d, the G‑d of Israel." The Sifri9 says, "The verse says, 'as commanded [to their father Aaron,] as com­manded by G‑d, the G‑d of Israel.' Where were they com­manded? In the verse, 'He did not give [any wagons] to the de­scendants of Kehos [since they had responsibility for the most sacred articles,] which they had to carry on their shoulders.' " This10 shows that it [carrying the ark on the shoulders] is counted among the mitzvos.