Why did Jesus tell His disciples to buy a sword? At the Last Supper, Luke records this dialogue:

He said to them, “But now if you have a purse, take it, and also a bag; and if you don’t have a sword, sell your cloak and buy one. It is written: ‘And he was numbered with the transgressors’; and I tell you that this must be fulfilled in me. Yes, what is written about me is reaching its fulfillment.”
The disciples said, “See, Lord, here are two swords.”
“That is enough,” he replied.

Luke 22:36-38
Why did Jesus tell them to buy a sword? And what should we make of His reply, &quot;That is enough&quot; when they produce two swords? Did He mean, &quot;that is enough talk&quot; or &quot;those are enough swords&quot;?
Up until this point, the disciples had operated under the aegis of both Roman and Jewish law.  They were seen as just another group of disciples of some charismatic Rabbi.  If he had some strange ideas he was teaching, well, so did plenty of others.

But now, all that was about to change.  He was going to be taken by the Jews, tried and convicted and put to death by the Romans.  Suddenly their Master's public status was about to go from "eccentric Rabbi" to "criminal condemned for stirring up trouble with the Romans," which would turn those who supported him into fugitives, at least temporarily.

Here, he was trying to explain to them that they would need to be prepared to stay mobile (side note: the word fugitive comes from a Latin root meaning "to flee"): they would  need to always have a purse (for money) and a bag (to carry basic supplies) ready, and that a sword (for protection against other men) was to be more important to them than a cloak (for protection against the elements) in the days to come.

But as we see repeatedly throughout the Gospels, the disciples never really "got" the whole "Jesus is going to die and then be resurrected" thing until after it was all accomplished.  Here, they hear him talking about swords, and someone says "yeah, we've got a couple here already."  They just don't understand what he's trying to explain, and you can almost hear the Master's resigned sigh.  "Sure, that'll be fine."