As the northern kingdom of Israel anticipating fighting an enemy, the Bible says:
So the king of Israel went with the king of Judah and the king of Edom, and they marched on that roundabout route seven days; and there was no water for the army, nor for the animals that followed them.
– 2 Kings 3.9
Since this is the Bible and sometimes the number 7 has a symbolic reference, we are tempted to signify every reference to 7 as being symbolic, but in this case, I see no reason for doing so.
This is simply an incidental reference to seven.