Ye have heard that it was said by them of old time, Thou shalt not commit adultery: But I say unto you, That whosoever looketh on a woman to lust after her hath committed adultery with her already in his heart. And if thy right eye offend thee, pluck it out, and cast it from thee: for it is profitable for thee that one of thy members should perish, and not that thy whole body should be cast into hell. And if thy right hand offend thee, cut it off, and cast it from thee: for it is profitable for thee that one of thy members should perish, and not that thy whole body should be cast into hell. (Mt. 5:27-30)
I used to work at a big company with some immoral co-workers, one of whom knew the Bible fairly well (a liberal, "nominal" Jehovah's Witness, believe it or not)...but he would check out some of the women in our big office. When he talked with me about that one time, I mentioned I didn't do that because Jesus talked about not lusting after a woman in my heart....and I was then called a legalist for my interpretation. His argument was that he wasn't "lusting" because he didn't actually want to have sexual relations with those women, but he just wanted to check them out ("appreciate their beauty").
His remark totally caught me off guard as I thought everyone knew what "lust" means (impure thoughts), but it also confused me in how to correctly respond with a correct definition of "lusting after." What would be the best way to respond to show what Jesus meant by looking at a woman "to lust after her"? (in other words, that "lusting after" would be a word regarding purpose, not only just result)