And He healed the poor soul that had his ear cut off. And the disciples had two swords between them. I do not recall anywhere in the book of Acts or the epistles where any believer used a sword to defend himself. I don't know why Jesus instructed the disciples to get swords.
The equivalent to an AR15 in those days would not be a sword. It would be a ranged weapon, such as a Ballista or at least a bow and arrow.
Poor soul? He was there to capture and kill Jesus. That damned soldier was on the wrong side. He should have fallen on his face before the King to beg for forgiveness. Had he believed on Jesus, he would have been saved.
Like other times, Peter didn't understand the circumstances. He misused his weapon trying to defend Christ from His mission, to die for the sins of all humanity. He stated this in 22:37
Then said he unto them, But now, he that hath a purse, let him take
it, and likewise
his scrip: and he that hath no sword, let him sell his garment, and buy one.
37For I say unto you, that this that is written must yet be accomplished in me, And he was reckoned among the transgressors: for the things concerning me have an end.
A. The command to buy a sword was not given to soldiers, law enforcement or security forces. This was to His disciples.
B. The reason is because He was going to be reckoned among the transgressors. What this means is explained in the next chapter.
32And there were also two other, malefactors, led with him to be put to death. 33And when they were come to the place, which is called Calvary, there they crucified him, and the malefactors, one on the right hand, and the other on the left.
Because of false teaching by the rabis and teaching priests, the Jews not only expected the Messiah to conquer their enemies but to rule as their King on Earth. There are prophesies we all know to this in more details about the end times of His second return. After that there will be peace and no need for assault or any other weapons of war. The only verse the united nations security forces quote is the one from Isaiah's prophecy concerning pounding their swords into plowshares, Isaiah 2:4, with their icon of a revolver with the barrel tied in a knot. That's a civilian weapon.
They are working towards having a monopoly of force, to conquer the world and disarm the people. What happens after peace keepers do that is to kill their enemies. The last century teaches us that.
The Lord's first advent was not to bring peace, but to make the way for all to have the opportunity of receiving His gift of life. When someone tries to steal that life as a murderer, He gives everyone the right to defend themselves. The Sword is an equalizer that helps to defend us from the evil.
He gives that right to every decent person to defend their people.
He did not bring peace and is not ruling earth with His rod of iron.
He provided the command to purchase the means to defend our loved ones in this hideously violent world.
Why did He command them to buy a sword?
Answer: Because He was to be reckoned among the transgressors.
There would be no peace until He establishes it Himself. In the meantime, buy a sword.