Fighting a common enemy is a very tough thing.
It needs enormous energy, resources and an united effort to beat an enemy. Enemies are there in our life at every step. And, if a country, a community and a society is not united it cannot fight an enemy successfully. This goes like theory that unless people are united themselves they cannot fight an outside force. It has been seen several times that when there was an external threat to a certain country, the country showed greater degrees of unity. But in some cases this unity was absent. In the absence of the unity those countries failed in their mission to fight the external enemy.
Here goes the important thing – if that country would have behaved in united way they could have been successful in beating the enemy. Since the country itself divided in its common goal, the defeat and the debacle was bound to come. So it came. That is why we say united we stand and divided we fall. In the same way, the Bible tells us to unite our house if we have to stand the time and adversities of the life.
If we have divided ourselves we would not be able to stand the time. The Bible suggests us to first arrange and unite our house so that the house could sustain the worst of the time. But when the house itself is divided it would not be able to sustain the blow of external dangers. And ultimately it will collapse.