“Whoever looks at a woman to lust for her has already committed adultery with her in his heart” (Matthew 5:28, NKJV). Jesus isn’t loosening the definition of adultery here, He’s widening our understanding of where sin actually begins. Not just in what we do, but in what we allow ourselves to dwell on.
That’s harder than it sounds. It would be simpler if holiness were only about outward behavior, the things other people can see and judge. Jesus removes that hiding place. A person can technically keep every visible rule and still have a heart that’s far from Him.
This isn’t meant to produce shame or a mental checklist of every wandering thought. It’s an honest invitation to notice patterns, what we dwell on, return to, or feed, and to bring those patterns to God rather than pretending they aren’t there.
The point of this kind of conviction isn’t condemnation, it’s growth. Jesus is describing the depth of the problem so that we’ll seek the depth of the solution, a renewed heart, not just better behavior on the surface.