דברי הימים א, פרק כ״ג, פסוק כ״ה

For generations, the Levites were tasked with the heavy physical labor of transporting the Tabernacle through the wilderness. A major shift occurred during David's reign, as he began counting the Levites for service starting at the age of twenty. This marked a significant change from the original law in the Torah, which required them to be thirty years old to begin their duties [מצודת דוד].

This adjustment in the age requirement reflected a new reality for the nation. God had finally granted peace and stability to the Israelites, bringing an end to their long era of wandering and constant movement [ביאור שטיינזלץ]. With this newfound rest, God established His presence in Jerusalem permanently, never to be moved again. Because His presence was now fixed in one location, the original work of the Levites, which involved carrying the Tabernacle from place to place, was no longer necessary [מצודת דוד].