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 eye is the lamp of the body. So, if your eye is healthy, your whole body will be full of light, 23 but if your eye is bad, your whole body will be full of darkness. If then the light in you is darkness, how great is the darkness! 24 No one can serve two masters, for either he will hate the one and love the other, or he will be devoted to the one and despise the other. You cannot serve God and money.
Sandwiched between the command to lay up treasures in heaven (6:19-21) and the warning that you can't serve God and money (6:24) are the strange words about the eye being the lamp of the body. If the eye is good (literally: "single"), the whole body will be full of light. But if the eye is bad, the body will be full of darkness. In other words: How you see reality determines whether you are in the dark or not.
Now why is this saying about the good and bad eye sandwiched between two teachings on money? I think it's because the specific thing about seeing that shows the eye is good is how it sees God in relation to money and all it can buy. That's the issue on either side of the sandwich meat. In 6:19-21 the issue is: you should desire heaven-reward not earth-reward. Which, in short, means: desire God not money. In 6:24 the issue is whether you can serve two masters. Answer: You cannot serve God and money.
This is a double description of light! If you are laying up treasures in heaven not earth, you are walking in the light. If you are serving God not money, you are walking in the light.
Between these two descriptions of the light Jesus says that the eye is the lamp of the body and that a good eye produces a fullness of this light. So what is the good eye that gives so much light and the bad eye that leaves us in the dark?
One clue is found in Matthew 20:15. Jesus has just said, in a parable, that men who worked one hour will be paid the same as those who worked all day, because the master is merciful, and besides, they all agreed to their wage. Those who worked all day grumbled that the men who worked one hour were paid too much. Jesus responded with the words found here in Matthew 6:23, "Is your eye bad because I am good?"
What is bad about their eye? What's bad is that their eye does not see the mercy of the master as beautiful. They see it as ugly. They don't see reality for what it is. They do not have an eye that can see mercy as more precious than money.
Now bring that understanding of the "bad eye" back to Matthew 6:23 and let it determine the meaning of the "good eye." What would the good eye be that fills us with light? It would be an eye that sees the Master's generosity as more precious than money. The good eye sees God and his ways as the great Treasure in life, not money.
You have a good eye if you look on heaven and love to maximize the reward of God's fellowship there. You have a good eye if you look at Master-money and Master-God and see Master-God as infinitely more valuable. In other words, a "good eye" is a valuing eye, a discerning eye, a treasuring eye. It doesn't just see facts about money and God. It doesn't just perceive what is true and false. It sees beauty and ugliness, it senses value and worthlessness, it discerns what is really desirable and what is undesirable. The seeing of the good eye is not neutral. When it sees God, it sees God-as-beautiful. It sees God-as-desirable.
That is why the good eye leads to the way of light: laying up treasures in heaven, and serving God not money. The good eye is a single eye. It has one Treasure. God. When that happens in your life, you are full of light.
Praying for the good eye with you,