Galatians 5:17: "The desires of the flesh are against the Spirit, and the desires of the Spirit are against the flesh, they are opposed to each other"

When a sinner, who was dead in his sin, is made alive in Christ, then the new heart has a newfound love, and so longs to please Jesus, the One who died for us. However, our flesh still wants to fight for self, and hates to deny itself. It's as if we are on a battlefield, and at war.
The Spirit calls us to deny ourselves. And so the battle goes forth. The struggle continues, and will continue until the Lord returns, or we "give up the ghost".

Hear what Jerry Bridges says: "We experience this struggle between the desires of the flesh and the desires of the Spirit daily. This tension causes us to sometimes wonder if the Gospel really does address this aspect of sin's power--that is, its ability to pull us toward its desires. This seems especially true in the more resepectable sins in our lives. Some of these subtle sisn seem tenacious, and we battle them daily. With others, we sometimes think we've turned the corner on one, only to discover a few days later that we've only gone around the block and are dealing with it again.

Paul's answer...."I say, walk by the Spirit, and you will not gratify the desires of the flesh." ....As we seek to walk by the Spirit, we will, over time, see the Spirit working in us and through us to cleanse us from the remaining power of sin in our lives. We will never reach perfection in this life, but we will see progress. It will be incremental progress, to be sure, and sometimes it will appear to be no progress at all. But if we sincerely want to address the subtle sins in our lives, we may be sure the Holy Spirit is at work in us and through us to help us.

How the Holy Spirit works in us and through us is a mystery in the sense that we cannot comprehend of explain it. We simply accept the testimony of Scripture that He dwells in us and is at work in us to transform us more and more into the likeness of Christ (see 2 Corinthians 3:18)."

And even sometimes when we cling to our pride, lust, or whatever sin, the Lord has ways to break us: "For whom the LORD loveth He chastens." Proverbs 3:12

Be encouraged if you are a child of God. The Father loves you very deeply. For He gave His beloved Son to secure you, and bring you out of the darkness, and into His kingdom of light. And He corrects each of us, and will never let us go. What a Father we do have.