At first glance, Jesus Christ seems to be commanding His followers to sell even their clothing, if necessary, to buy weapons. But if we examine this scripture more closely, as well as the preceding and following events, we can better understand His instruction.
Christ first asks the disciples if they were provided for when He sent them out. His reference to an earlier event provides the background for the commands in Luke 22 (see the notes at Matthew 10:7-10). Jesus' earlier instructions—when the disciples were sent out as ambassadors to announce the presence of a King and a Kingdom—are distinctly different from these later instructions just before His death and resurrection, when He would no longer be with them in person.
With this background in mind, we can see the contrast in Christ's instructions, and how His death would require a change in approach for the disciples as they conducted His work.
In Luke 22, Jesus first calls to their attention that they were divinely provided for during His earthly ministry. They did not lack anything. He is reiterating that they will still be provided for, but their circumstances would not be as comfortable as before. They would have to trust even more and perhaps be satisfied with less. God would still provide for them, simply because it is a fundamental part of His nature, but things would not be as easy.
We can see this principle at work in the account of the first Pentecost after Christ's ascension. There were many signs and miracles, and undoubtedly every person present remembered that day for the rest of his life! As the church started out, there were miraculous healings and other gifts of the Spirit being manifested seemingly on a regular basis. However, when we read the accounts of the apostles later in their lives, there are no records of the same public miracles or healings.
Had God left them? Was He displeased with their work? Had they lost their faith? Was He limiting their supply of His Holy Spirit? On the contrary, the apostles were maturing spiritually, and God did not need to bolster their faith in the same way through astounding manifestations of His Spirit. "Elementary school" was over. Now they were growing up spiritually and had more serious work to do.
In the same way, Christ warned the disciples in Luke 22:36 that their responsibilities would be increased, their journeys lengthened, the dangers greater, and the physical costs higher. God would still be with them, but they would begin to be more acutely aware of their physical circumstances and have to trust in Him to an even greater degree.
Christ's instructions in verse 36 are primarily spiritual, but there are true physical principles in them as well. The disciples would be going on much longer and more arduous missions now, and they would have need of a moneybag and knapsack. But shortly after His original instructions to the disciples in Luke 9:3 and Luke 10:4, He showed them that material wealth is of little importance:
Sell what you have and give alms; provide yourselves money bags which do not grow old, a treasure in the heavens that does not fail, where no thief approaches nor moth destroys. For where your treasure is, there your heart will be also. (Luke 12:33-34)
Yes, they would have need of bags to carry their provisions, but again, Christ teaches them not to be limited to the physical and temporal in their contemplations. It was exceedingly more important that the "bags" the disciples carried with them be spiritual moneybags, symbolizing good works that would never decay or be stolen. While there was a physical application of His instruction, the real lesson was a spiritual one.
In the same way, Christ's instruction to buy a sword had an immediate application in that it would fulfill in part the prophecy of Isaiah 53:12: By carrying weapons, the disciples would be classified by others as transgressors or criminals. In this instance also, the spiritual application far outweighs the physical.
The disciples' reaction shows that they did not really grasp His intent. Their response is, "Lord, look, here are two swords," to which He replies, "It is enough." He is not saying that two swords would be enough to defend twelve men. If that were His intent, He would have said, "They are enough." Instead, He is showing that the discussion was over. It was a mild rebuke showing that the matter was closed, as in "Enough of this!"
Through His capture and trial, Jesus Christ demonstrates that neither He, nor the disciples, nor anyone following Him, needs to take up a weapon:
But Jesus said to [Judas], "Friend, why have you come?" Then they came and laid hands on Jesus and took Him. And suddenly, one of those who were with Jesus [Peter (John 18:10)] stretched out his hand and drew his sword, struck the servant of the high priest, and cut off his ear. Then Jesus said to him, "Put your sword in its place, for all who take the sword will perish by the sword. Or do you think that I cannot now pray to My Father, and He will provide Me with more than twelve legions of angels?" (Matthew 26:50-53)
The parallel account in Luke 22:49-51 shows that Christ was so opposed to this sort of violent reaction by Peter that He miraculously undid what Peter had done!
Peter was walking by sight. He did not yet grasp that God was completely in control; nothing would happen to him or to Jesus that was not according to God's ultimate plan. God's plan entails so much more than just length of days or freedom from injury! This physical life is the training ground, not the end. One who stays faithful to his commitment to God will not die until God's purpose for him is complete!
It is given that all men die (Hebrews 9:27), and our death may even be a violent one—of all of the apostles, only John died a natural death. As servants of God, we can expect to be persecuted in the same way our Master was (II Timothy 3:12). But that does not give us cause to take up arms if it means harming someone else! Christ shows that those who trust in physical protection will be let down, while those who trust in God to defend them will never suffer anything that does not ultimately fulfill His purpose.
Jesus Christ's words in Luke 22:35-37 are not instructions for us to be physically armed or to trust in our own might for our physical defense. There will always be a weapon or a foe that is stronger than any physical defense we could muster. God tells us to stay above the fray and to trust in Him for our defense.
If He sees fit to let persecution or injury befall us as a consequence of our own foolishness or sin, we should learn from our mistake and continue on. However, if we are reviled, slandered, or even physically persecuted for righteousness' sake, and we take it patiently—that is, if we endure it without reaching for a sword—this is commendable before God (I Peter 2:19).