Three sayings sit back to back, and they look like three topics: treasure, eyesight, and employment. They are one argument said three times, each time a layer deeper.
Start with the treasure. Wealth in that world was never as secure as banks make it feel. Fine clothing, a common store of value, fell to moths. Metal corroded. And houses of mud brick gave a determined thief a wall to dig through, and no door needed picking. 19"Do not lay up for yourselves treasures on earth," Jesus says, naming a vulnerability every listener knew from experience. Heaven has none of it, and Jesus says so in the next verse: 20"where neither moth nor rust destroys and where thieves do not break in and steal." Then he adds 21"where your treasure is, there your heart will be also," which describes what is already true. Your heart is following your treasure right now, wherever you have quietly decided to put it.
What does it mean to lay up treasure in heaven? Elsewhere Jesus ties it to giving: "Sell your possessions, and give to the needy. Provide yourselves with moneybags that do not grow old, with a treasure in the heavens that does not fail" (Luke 12:33). Treasure in heaven moves in one direction, out of your hands and into someone else's need, and heaven keeps the record. That is why the heart follows it. The person who gives away part of a paycheck to a need finds attention going after it. The person who hoards finds attention fixed on the pile. Where the money goes, the attention goes.
Then the eye. 22"The eye is the lamp of the body." In the ancient view the eye sent light out into the body, and Jesus says a healthy eye fills the body with light while a bad one fills it with darkness. The Greek word behind "healthy" means single, undivided. Elsewhere it carries the sense of generosity, and the opposite, a bad eye, meant stinginess. Both meanings work together here. A heart with one loyalty is almost automatically a generous heart. A heart split between two loyalties squints at everything and everyone through the same divided lens.
Then the masters, and the language gets stronger than a choice between priorities. The word for "serve" describes what a slave does. You can hold two jobs, and you cannot belong entirely to two owners. 24"You cannot serve God and money." "Mammon" was an ordinary Aramaic word for property. Jesus personifies it as a rival master because money is uniquely suited to become the thing a heart trusts for security, in the place only God was meant to occupy.
Treasure, eye, master: three pictures of one fact. A heart cannot split its ultimate loyalty the way a schedule splits its hours. Jesus keeps returning to the point until it becomes impossible to miss.
Ask where your attention goes when nobody is asking. Follow that trail to the treasure. Then decide whether the heart that has followed it is where you want it to be.
Prayer
Father, thank you that you ask for our whole and undivided loyalty. Show us where our treasure is. Teach our eyes to be single and generous. Free us from trusting money for the security only you can give, and let our whole life be lit by one undivided love for you. In Jesus' name, amen.