דברי הימים ב, פרק י״ג, פסוק י׳

A sharp contrast exists between the faithful traditions of the Kingdom of Judah and the practices of those who abandoned their spiritual heritage. The people of Judah maintain the complete, proper structure of Temple worship, which rests on three core elements: the One being worshipped, the workers, and the work itself [מלבי״ם].

Unlike those who have strayed, the people of Judah declare their absolute loyalty to God. They affirm that He is their God and that they have never forsaken Him [מצודת דוד, רלב״ג, ביאור שטיינזלץ]. The legitimate service in His house is carried out strictly by the rightful workers, who are exclusively the priests descending directly from Aaron.

The work itself is performed by the Levites, who are fully engaged in their designated duties exactly as King David originally established them [רש״י]. Every individual stands firmly at his assigned post. Some serve as gatekeepers, while others are entrusted with the musical service, using their voices and playing instruments to offer thanks to God [רש״י, רלב״ג, רד״ק, מצודת דוד, מלבי״ם].