John 18:10-11.
Then Simon Peter having a sword drew it, and smote the high priest’s servant, and cut off his right ear. The servant’s name was Malchus.
Then said Jesus unto Peter, Put up thy sword into the sheath: the cup which My Father hath given Me, shall I not drink it?
Peter simply couldn’t stand by and watch while his Master was arrested! A man of action for his entire life, he pulled his sword out of its sheath and attached Malchus, the servant of the High Priest. Malchus must have put up a good bit of resistance, for all that Peter was able to do was to slice off his ear.
I was surprised at the amount of commentary I found on this act of Peter. Some have construed it to have a great deal more meaning than others: Since Malchus was a servant (slave) of the High Priest, Peter was symbolically attacking the religious authority of the day; that it was cowardice on Peter’s part, since, if he were holding the sword in his right hand, he could only have cut off the right ear from behind; and many other ideas which seem to me to be stretching the importance of this act.
Rather, I’m thinking Peter was remembering his promise that he would go even unto death in defense of Jesus (Matt. 26:35) and that his attack was impulsive and carried out on the nearest victim.
Some have wondered why any of the disciples carried a weapon. It is probable that Peter’s sword was a short sword, not the long one of the centurions; that it was easily concealed by his clothing; that it had to do with his work as a fisherman. Also, this was a time, like our own, when thieves and murderers were ubiquitous. Having some sort of weapon was only common sense.
John doesn’t tell us the rest of that small moment, but Luke 22:51 does. Jesus rebuked Peter (“Suffer ye thus far!” In other words, “That’s enough!”) and He touched Malchus’ ear and restored it.
He then addressed Peter again, telling him to sheath his sword, and saying, “You must not try to keep Me from doing the work that the Father has appointed to Me. The time has come. There will be no more avoiding the priests and the Pharisees.”
Linda's Bible Study 
I agree with your idea that Peter acted impulsively and whacked at random.
As Peter’s sword, I’ve heard it explained this way:
Jesus asked the disciples before they left the upper room, something like: “Do you have a weapon/sword?” And they said, “Yes, here are two.” And Jesus said, “It is enough.”
Jesus knew full well what he was facing, that soldiers would come for him. He knew that two swords would be like toothpicks against an armed mob. Yet he said, “It is enough.”
And it was enough for the demonstration. Jesus didn’t want swords clashing and his disciples hurt. As soon as the sword was used, He told Peter, “Put up your sword. They that take the sword shall perish by the sword. The cup my Father gave me to drink, shall I not drink it?” (I’m quoting from memory here, so please allow room for error.)
Then He healed the injured man; another demonstration that He came “to seek and to save,” not to lead an insurrection. So one sword was enough for the object lesson He taught that night. As He said later to Pilate: “I could call ten thousand angels…but my kingdom is not of this world, or else my servants would fight to save me.”
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Thanks, Christine. Your quote is close enough š
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One other thought: I’ve wondered if Malchus was named, not just “a servant” because he was known to the church and John’s readers. That is, he became a believer, too.
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That’s a strong possibility. Perhaps Peter was the one who led him to Jesus :). Also, he was more than a servant, from what I understand. The Greek word can also mean “slave.”
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