A.T. Robertson Commentary Luke 22:36

"And he said unto them, But now, he that hath a purse, let him take it, and likewise a wallet; and he that hath none, let him sell his cloak, and buy a sword." — Luke 22:36 (ASV)

Buy a sword (αγορασατω μαχαιραν). This is for defence clearly. The reference is to the special mission in Galilee (Luke 9:1–6; Matthew 9:11–35:1). They are to expect persecution and bitter hostility (John 15:18–21). Jesus does not mean that his disciples are to repel force by force, but that they are to be ready to defend his cause against attack. Changed conditions bring changed needs. This language can be misunderstood as it was then.