Why would Jesus tell them to buy a sword?
*And He said to them, “When I sent you without money bag, knapsack, and sandals, did you lack anything?”So they said, “Nothing.”*Then He said to them, “But now, he who has a money bag, let him take it, and likewise a knapsack; and he who has no sword, let him sell his garment and buy one. *For I say to you that this which is written must still be accomplished in Me: ‘And He was numbered with the transgressors.’ For the things concerning Me have an end.”*So they said, “Lord, look, here are two swords.”And He said to them, “It is enough.” - Luke 22:35-38
http://www.biblegateway.com/passage/?search=Luke22:35-38&version=NKJV