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.