"Good Eye" vs. "Bad Eye"
The Jewish idiom of the "good eye" refers to loving and taking care of your neighbor, while the idiom of the "bad eye" refers to being selfish and not loving your neighbor. This can be seen in the words of Yeshua:
MATTHEW 6:19 "Do not lay up for yourselves treasures on earth, where moth and rust destroy and where thieves break in and steal;
20 "but lay up for yourselves treasures in heaven, where neither moth nor rust destroys and where thieves do not break in and steal.
21 "For where your treasure is, there your heart will be also.
22 "The lamp of the body is the eye. If therefore your eye is good, your whole body will be full of light.
23 "But if your eye is bad, your whole body will be full of darkness. If therefore the light that is in you is darkness, how great is that darkness!
24 "No one can serve two masters; for either he will hate the one and love the other, or else he will be loyal to the one and despise the other. You cannot serve God and mammon. (NKJV)
Most Bibles indicate a change of topic at verse 22 and again at verse 24. However, there is no change of topic in this passage. Having a "good eye" corresponds to storing up treasure in heaven, while having a "bad eye" corresponds to storing up treasure on the earth.
Those who have a "good eye" serve God by loving their neighbor and using their material goods to take care of them. Those who have a "bad eye" serve "mammon" (material things) and selfishly hoard their earthly treasure instead of serving their neighbor with it.