One of the realities of the Christian life is that we sin. Of course there is abundant grace to overcome sin, but guilt-ridden souls need a remedy. The greatest problem for many believers is not the fact that they sin, but that they are consumed with guilt.
Of course, conviction from God is right. If we sin, it is right that we know we have grieved the Lord. We need to confess and repent of our sin, but we also need to rejoice in the knowledge that He is "faithful and just to forgive us our sins" and that "we have an advocate with the Father, Jesus Christ the righteous. And He Himself is the propitation for our sins..." (1 Jn 1v9, 2v1-2).
But if we don't grasp this, then we can become consumed with guilt. I remember a friend who years ago was due to share a short word one Sunday evening. He came to me on Sunday morning asking me to pray for him because he didn't feel he could speak in the evening because he sinned the day before.
Guilt keeps us away from intimacy with the Lord. Intimacy with the Lord is one of the greatest helps in resisting temptation - superior pleasure. Guilt can lead to a subtle reliance on works rather than grace. "If I fall, I can't pray, worship, serve, preach, witness until I have really worked hard on my relationship with God." Many believers think like this.
Worse still, joy and passion declines, a believer listens to the lies of the enemy and feels completely useless. The long term result is a slow slide into mediocrity.
I have found a hugely helpful transcript of a message by John Piper. While the message deals specifically with sexual sin, I actually believe it is helpful for every single child of God who struggles with guilt.
I strongly recommend reading it. I'm going to run off lots of copies and share it in our church (I hope John Piper won't mind!).
Freedom from guilt means that if we sin, we don't wallow for hours or days, but we confess, repent, seek fresh grace from God and return to service in His purposes straight away. No time wasted, a return to fellowship with the Lord and joyful service - which is a further protection against falling again.