Albert Barnes Commentary 2 Chronicles 29:27

"And Hezekiah commanded to offer the burnt-offering upon the altar. And when the burnt-offering began, the song of Jehovah began also, and the trumpets, together with the instruments of David king of Israel." — 2 Chronicles 29:27 (ASV)

Everything up to this point had been preparatory. Now Hezekiah gave orders that “the burnt offering”—that is, the daily morning sacrifice—should be offered on the bronze altar in front of the porch, thereby restoring and re-instituting the regular temple service. A burst of music announced to the people the moment the old worship resumed.