Imagine yourself at home alone with a beautiful girlfriend, sitting on the couch. She leans towards you, gazes into your eyes, and your heart begins to race. You love each other deeply and have been together for a long time. How far should you go? Where do you draw the line?

Before you answer the question, let's change one detail of the scenario. Instead of you and your girlfriend, let's say the guy is someone you hardly know and the girl is your little sister. Now, where did you say you wanted to draw the line?

You guard your sister's innocence because you love her. Why don't we do the same for the girlfriends we claim to love so deeply? We have all kinds of reasons to justify our actions. We tell ourselves, "She's okay with it," "It's not like we're going all the way," or "I can see myself marrying her one day." If you've convinced yourself that a form of physical affection is okay, try picturing the expression on her dad's face if he walked into the room while you were doing it.

The bottom line is this: Until her father gives you her hand in marriage, he is her man. Although my wife's dad abandoned her when she was little, her foster-father walked her down the aisle on our wedding day, gave me a firm handshake, and entrusted her to me. Honor a girl's dad in the same way you will want to be honored when it's your daughter going to the prom with a teenage guy you barely know. Ask yourself: Would I want a guy like me dating my own daughter? Or my sister?

If you are being called to marriage, imagine that your future wife is on a date right now with a guy you'll never meet. How far would you like the two of them to go? Odds are that you'd like her to be just as pure after the date as she was before it.

Most guys—if they're honest with themselves—will admit that they have one standard for their sisters, future wives, and future daughters but an entirely different standard for themselves. To avoid this double standard, treat girls the way you would want a guy to treat your future bride. Then, even if a relationship doesn't work out, your girlfriend will be a better person for having dated you. She won't feel regretful or resentful. She'll be closer to God and to her family, not alienated from them.

These guidelines may clarify some things, but they don't get to the heart of the matter. If we love girls, why would we ask how close to sin we can get them? We should be more interested in how close to God we can lead them. Purity is not about following a list of rules so that we'll avoid hell. It's about wanting heaven for the women we love.