What is lust and why do we lust?

According to my knowledge of the Word of God, lust is a sin in the simplest way of understanding what it is according to the Word of God. It's part of the Sin Nature or the Old man's ways because it's ungodly and sinful to lust after a woman or women in your heart. But it can be worse than that it can lead to several ways of undressing women in your mind. For instance, if a man is over-fantasizing, dreaming, reminiscing, and many other things to please his sexual craving for sex. Lust can lead to just more than having these things in the mind but also seeking to fulfill them by finding and sleeping with women or watching these things. Watching or having anything outside of marriage is lust and is a sin. You’re not supposed to marry just to do that because it's seeking fulfillment of desire and marrying what you're idolizing. You marry them with the idea that your cravings will be met timely and often as needed. That is an abomination in the sight of God. You can not live in sin and be comfortable living in sexual immorality. Do not misunderstand that sex is a sin, but having sex in your heart or with someone outside of marriage is a sin. Sex is only for a man and a woman who are evenly yoked as believers under a covenant with God. This is how we know sex is a gift or a blessing from God and is pleasing in His sight.

Salsanblues a Reddit user stated:

"Feeling attraction is not sinful. Feeling sexual desire is not sinful... None of these things are sinful on their own, they are part of God's design. Lust, in its most basic, is the objectification of another person for your selfish pleasure. It's a one-sided sexual act/fantasy that you CHOOSE, which is outside of the consent of the other party. They keep teaching men that they are no better than animals and that acknowledging attraction or sexual interest is lust. It's not. Then they tell women that it's their responsibility to prevent the men around them from lusting and that their bodies insight lust. (My comment "A woman is responsible for her appearance aka modesty and speaks.) Which is reducing women to the sum of their body parts instead of seeing them as whole people, worthy of respect and sisters in Christ. When you see a super attractive woman in the street, or on the bus, just living life, it's fine to acknowledge that she's attractive. But lust is when you stop caring about her as a person, see her body as something to consume, and use her for your pleasure regardless of her consent.

It is important as a man to note that you can be sexually attracted to women but if you do not have the Spirit of God in you then you will be lusting after them. If you're struggling as most you need to ask Jesus to cause you to stop lusting after women and bring all imaginations to death with that old man at the Cross. Let the Holy Spirit lead you to the Cross and accept your death to sin and rise putting on your new man in Christ. Your freedom or victory over lust is in Christ, which means you must believe the Word, and accept Christ living in you and through you. Your faith must be ground on the rock, which Christ, He is the rock of the believer." Salsanblues

Note: this is not the original, so no man may stumble.