The journey back to Jerusalem requires not only physical protection but spiritual responsibility, especially when transporting the treasures of the Temple. Ezra addresses the leaders of the priests [רש״י], officially entrusting them with the care of these sacred items.
The primary approach among commentators is that a fundamental parallel exists between the carriers and the objects they carry. Just as the Temple vessels are holy to God, the servants of the Temple—the priests and the Levites—are equally holy to Him [רס״ג, רלב״ג, ביאור שטיינזלץ]. This shared sanctity provides the underlying logic for why Ezra places the treasures specifically in their hands. It is only fitting that sacred objects be given to and held by sacred individuals [מצודת דוד, ביאור שטיינזלץ, רלב״ג].
This declaration of their holiness is not merely a description of their status; it carries a strict practical duty. Because they are holy, they are bound to guard the treasures with intense care [מלבי״ם]. They must watch over these items continuously until they arrive in Jerusalem, where the treasures will be safely weighed in the chambers of the House of God before the leaders of the priests, the Levites, and the heads of the Israelite families [רלב״ג]. Furthermore, the silver and gold being transported are voluntary donations given to God. This detail emphasizes that even these freewill offerings hold the exact same status of absolute holiness as any other sacred item [מצודת דוד].