22 The light of the body is the eye: if therefore thine eye be single, thy whole body shall be full of light.
23 But if thine eye be evil, thy whole body shall be full of darkness. If therefore the light that is in thee be darkness, how great is that darkness!
I used to think this was about sanctification in a general sense, that what you look at affects you. But when you connect it with the Old Testament, the meaning gets more specific.
In Hebrew, “evil eye” and “good eye” are idioms about money:
22 He that hasteth to be rich hath an evil eye, and considereth not that poverty shall come upon him.
9 He that hath a bountiful eye shall be blessed; for he giveth of his bread to the poor.
“Bountiful eye” is literally “good eye” in Hebrew. An evil eye is a greedy person. A good eye is a generous one.
That changes what Jesus is saying. Look at the context, the verses right before and after:
19 Lay not up for yourselves treasures upon earth, where moth and rust doth corrupt, and where thieves break through and steal:
20 But lay up for yourselves treasures in heaven, where neither moth nor rust doth corrupt, and where thieves do not break through nor steal:
21 For where your treasure is, there will your heart be also.
(Our main study verses: 22 and 23)
24 No man can serve two masters: for either he will hate the one, and love the other; or else he will hold to the one, and despise the other. Ye cannot serve God and mammon.
And then He continues by saying we should not worry about food or clothing, but seek the Kingdom of God first:
31 Therefore take no thought, saying, What shall we eat? or, What shall we drink? or, Wherewithal shall we be clothed?
32 (For after all these things do the Gentiles seek:) for your heavenly Father knoweth that ye have need of all these things.
33 But seek ye first the kingdom of God, and his righteousness; and all these things shall be added unto you.
34 Take therefore no thought for the morrow: for the morrow shall take thought for the things of itself. Sufficient unto the day is the evil thereof.
The whole passage from verse 19 to 34 is one continuous thought about treasure, money, and trusting God. Verses 22-23 sit right in the middle of it.
Before them, Jesus says your heart follows your treasure. After them, He says you cannot serve God and money. So the “eye” in between is about how you relate to wealth. A single (good) eye means you are generous, your treasure is in heaven, and your life is full of light. An evil eye means you are greedy, your treasure is on earth, and darkness fills you.
The scariest part is the last line: “if the light that is in thee be darkness, how great is that darkness.” A greedy person thinks they are being wise or careful with money. They think their way of seeing the world is right. But Jesus says that “light” is actually darkness. And it is worse than regular darkness because the person does not even know they are blind.
So practically, how much am I worrying about money? How much of my focus goes toward career, salary, financial security? God wants me to depend on Him. He is not asking me to be irresponsible, but He is asking where my heart is. The command is to seek His Kingdom and His righteousness first, not my career first and God second.
And notice that the promise of provision in verse 33 is not unconditional. “All these things shall be added unto you” is tied to “seek ye first the kingdom of God.” The provision follows the focus. If my eye is single, if my heart is set on His Kingdom, He takes care of the rest. But if my eye is evil, if I am chasing wealth and worrying about tomorrow, I am serving mammon and calling it wisdom.