those who do wrong to others will themselves be hurt in the same way; violent people will be hurt by violence
—My uncle used to steal supplies from his office at work. Now that he owns his own business, he says that his biggest problem is theft by employees. Hmmm. You live by the sword, you die by the sword.

When Jesus was arrested by the authorities, Peter, one of his disciples, tried to defend him. He pulled out a sword and cut off the ear of a man who had come with the soldiers. Jesus rebuked Peter, telling him to put his weapon away:

Put your sword back in its place! For all who take hold of the sword will die by the sword [all they that take the sword shall perish with the sword]. Or do you think that I cannot call on my Father, and that he would send me more than twelve legions of angels right now? How then would the scriptures that say it must happen this way be fulfilled? (Matthew 26:52-54)

Jesus did not fight back. Instead he allowed himself to be arrested, fulfilling the Old Testament prophecies, such as those in Isaiah, which said that the Christ would willingly give up his life as a sacrifice for other’s sins.

Sometimes live by the sword, die by the sword is used with sword replaced by another word or phrase. For instance, we can say about a baseball pitcher that he “lives by the fastball and dies by the fastball.” In this usage, the meaning is “to stay with a strategy, even when it is no longer successful.”