Jesus says in Matthew 5 that if any one of us looks at a woman lustfully he’s already committed adultery with her in his heart. What does that passage mean for single people? Is it possible to commit adultery if you’re single? If you’re single, is it a sin to look at a woman lustfully?
The direct answer is: yes. It is a sin to lust after someone. Jesus is pretty clear about that one in this passage. You are right that it is an odd thing to talk about single people committing adultery. If you pull back the lens to look at what Jesus is saying in this part of the Sermon on the Mount, it makes a bit more sense.
In Matthew 5, Jesus talks about how his teachings relate to the Old Testament law. He says it is the fulfillment of that law, not the abolishment of it. It makes sense that He points that out first, because He says some revolutionary things.
He starts these sections, including the one on lust, by saying “You have heard it said” and then giving the Old Testament command that He is expanding upon. Look at those teachings He is reinterpreting for the crowd: don’t murder, don’t commit adultery, don’t get divorced, keep your word, be fair, and love your friends. If doing those things are what make you a good person, then most people are doing just fine.
But now look at the standard Jesus gives: don’t be angry with people, don’t look at people lustfully, don’t seek revenge, love your enemy. If that is that standard, then nobody can live up to that! That is exactly the point. We are in trouble if that is what it takes, and we need a savior. No wonder the people who hated Jesus most where the church people who just loved the idea that they were righteous all on their own.
At the core of your question seems to be the idea that it is impossible to ask someone to not lust, and you are exactly right. Jesus is saying that the standard is so high that you can’t possibly meet it, and that is okay. You are saved by grace and, by walking with your savior, you can grow little by little towards the life He wants for you.
-Matt from The Bridge