Pornography and Lusts of the Flesh
Based on what God has done for us, Paul is urging us to "cleanse ourselves from all filthiness of the flesh and spirit, perfecting holiness in the fear of God".
Trying to fulfill the lust of the flesh is a worthless endeavor. You can never satisfy your flesh. The flesh always demands more. Get a new car? Shortly you'll want another. Fly somewhere? You'll want to fly first-class. Fly first-class? You'll want to fly on a private jet. Fly on a private jet? You'll want to own your own private jet. It never ends.
There are so many lives and families that have been ruined by pornography. It's a fantasy world that promises fulfillment but always leaves people wanting more. In many cases it leads to people wanting "cosmetic surgery". That surgery leads to another. And another. In other cases it leads to a string of relationships which are ultimately based on sex. They typically end because the sex was not enough. Although the people are sure the next relationship will do it for them.
As Paul wrote, we need to cleanse ourselves from all filth and not allow the flesh to take over our lives. The key is the fear of God. If we have a healthy respect for God and know that he is always with us, it has a purifying effect on our lives. We should be afraid to do things that offend him.