The lords wanted to make sure that the ark left the land of Philistia and that it was received back in Israel. This is necessary to affirm whether or not their tribute to the Lord had been accepted by him and that he was responsible for their calamities.
12 And the cows went straight in the direction of Beth-shemesh along one highway, lowing as they went. They turned neither to the right nor to the left, and the lords of the Philistines went after them as far as the border of Beth-shemesh.