And when the ark... came into the camp. — As far as we know, this was the first time since the establishment of the people in Canaan that the Ark had been brought from the permanent sanctuary into the camp. The shout of joy represented the confidence of the army that now the Ark, which had witnessed so many splendid victories of the chosen race, was among them, discomfiture was out of the question.
Related Commentaries of 1 Samuel 4:5
1 Samuel 4:5
5 And when the ark of the covenant of the LORD came into the camp, all Israel shouted with a great shout, so that the earth rang again.