2 Chronicles 20:28

And they came to Jerusalem with psalteries and harps and trumpets unto the house of the LORD.

Before the battle Jehoshaphat called the people to believe in the Lord and to believe His prophets, and he appointed singers praising the beauty of holiness to go out before the army. When they began to sing, the Lord set ambushments against Ammon and Moab and Mount Seir, so that those enemies destroyed one another until Judah found only dead bodies with none escaped. God thus won the battle for Judah without Judah having to fight. Because the Lord had made them to rejoice over their enemies, Jehoshaphat then led every man of Judah and Jerusalem back to Jerusalem with joy. They entered with psalteries and harps and trumpets unto the house of the Lord in thanksgiving worship after God gave them victory over their enemies.

Their celebration followed their trust in God and His deliverance. They could therefore praise Him as their refuge and strength and righteous judge. After this return, the fear of the Lord fell on the surrounding kingdoms when they heard that the Lord had fought for Israel. God gave the realm quiet and rest round about.