Luke 11:17
But he, knowing their thoughts, said unto them, Every kingdom divided against itself is brought to desolation; and a house divided against a house falleth. But he, knowing their thoughts, said unto them, Every kingdom divided against itself is brought to desolation; and a house divided against a house falleth.
Every kingdom divided against itself is brought to desolation and ruin, and a house divided against itself falls and cannot stand or endure. Division within a kingdom leads to its ruin. In its setting this principle answers the charge that casting out demons was done by Satan's power, for Satan would not cast out his own demons since doing so would divide and undermine his own kingdom.
Applied to the church, division and bitter dissension weaken, damage and harm it, destroy the peace and harmony of churches, and hinder the cause of truth. Such division widens as people take sides and accusations multiply, with wrong feelings and uncontrolled words widening the breach into hostility. Mutual accusations multiply as the breach widens into hostility.
Division of this kind gives Satan an opportunity and opening to work, to divide and destroy. It also turns observers and onlookers away from religion and leads them to reject it. In doing so it confirms onlookers in impenitence.
Discord of this kind can also rend families and ruin hopes, warning that division brings destruction. The same image applies to evangelism when Christian societies compete for their own sects and oppose one another in places like Italy, presenting the gospel as divided against itself and weakening its witness.