It's not just that by using porn, you're exploiting another person and turning the human in the centerfold into a mere object.
All those points are true, of course, but the most essential truth of chastity is that in turning away from certain expressions of sexuality and romanticism, we can allow ourselves to focus on God in a particular way that would otherwise not be possible.
Tim and Jess had only been married for eight months, but the honeymoon was most certainly over. As I unpacked some of the couple’s history, I discovered he hadn’t sabotaged them on their honeymoon, nor in the early months of figuring out married life.
The sweet conversations that once marked their relationship had been replaced with constant bickering. The Devil had begun his work before they’d even made it to the altar.
So don't dress modestly or refrain from having premarital sex because doing so will help you attract the attentions of an upright, God-fearing Christian partner (though, of course, that might also happen) — dress modestly and refrain from premarital sex because doing so allows you to focus on your truest Lover, the Lord.
Practice chastity because, in the words of 6th-century monk John Climacus, "Chastity makes us familiar with God." I have written this article — indeed, I have written a whole book on the topic of chastity and sexuality — because I think chastity is a crucially important piece of Christian faithfulness and Christian discipleship.