The quote is part of a parable Jesus told to his disciples regarding the evil in humans, and is found in Luke 11:21-22:
"When a strong man armed keepeth his palace, his goods are in peace.

But when a (being? Beelzebub?) stronger than he shall come upon him, and overcome him, he taketh from him all his armour wherein he trusted, and divideth his spoils." (King James version)

Luke chapter 11 starts with teaching the Lord's prayer which we still speak today, and also the beautiful instruction "Ask, and it shall be given you; seek, and ye shall find; knock, and it shall be opened unto thee."

In other words, be generous to your friends, don't let evil into your life or it will overcome you and destroy you.

This parable isn't about guns, which didn't exist 2000 years ago, it is about avoiding evil in our dealings with others, lest evil overcome us.