They sang together by course. Literally, "They replied (to each other)," or sang antiphonically; the burthen of their song being, that God was good, and his mercy towards Israel everlasting. All the people shouted with a great shout.
Shouting on occasions of secular joy and triumph has been practised by most nations, both in ancient and modern times. But religious shouting is less common. Still we hear of such shouting when the ark of the covenant was taken into the Israelite camp near Aphek (1 Samuel 4:5), and again when David solemnly brought it up from Kirjathjearim to Jerusalem (2 Samuel 6:15).
Shouting appears also in the Psalms (Psalms 47:5) and in Zechariah (Zechariah 4:7) in connection with religion. It is always indicative of religious joy.