For those who do not believe the Gospel, the point of disconnect between them and those who are a part of the body of Christ is usually the doctrine of Justification.
What I mean is, those who have not repented of their sin and do not trust in Jesus' vicarious atonement for the forgiveness of their sin just don't understand how forgiveness works. They may be aware that something is wrong. They may feel that they are not right with God in some way. They may even want to correct this. The problem is that they don't know how. Their efforts to make themsleves right with God manifest in just that way...efforts to make up for all the wrongs they have done. It isn't until they hear and believe the Gospel that Christ died to atone for the sin of the world that we are brought to realize just how worthless our efforts to "make things right" are.
But what if you are a Christian and still troubled by your sin?
If by troubled you mean something like you are worried you committed a sin that is too terrible to be forgiven, there is an answer. Your brethren in Christ, and your faithful pastor have been given you by Jesus to hear your confession, and declare the good news that Jesus death has paid for all your sins, no matter what they are. In the case of your faithful pastor, he is there to hear your private confession; to give to you individually and without equivocation the forgiveness that Christ has won for you on the cross.
What if, however, you are troubled in a different way?
What if you already believe that your sins have been paid for by Christ, even the really, really terrible ones? What if, instead of being worried about not being forgiven, you are tormented by the fact that you committed terrible, maybe even unspeakable acts; that you harmed others? You know that you are forgiven by Christ, but you are sad beyond words that you have so greviously harmed your neighbor. You know that the guilt of your sin has been wiped away where God is concerned, but the remorse still presses upon your heart until it is crushed into despair.
Perhaps this despair is part of the suffering we must endure as part of our being a Christian.
Is the guilt and despair really due to fear of possible temporal consequences?
So, where is one to turn when one finds himself in such a situation?
I suspect the right answer to that last question is the same as it is for when one is worried about their salvation: Jesus.
When we are distressed, scripture encourages us to bring our troubles to God in prayer. Paul writes the following to the Philippians:
Rejoice in the Lord always. I will say it again: Rejoice! Let your gentleness be evident to all. The Lord is near. Do not be anxious about anything, but in every situation, by prayer and petition, with thanksgiving, present your requests to God. And the peace of God, which transcends all understanding, will guard your hearts and your minds in Christ Jesus (Philippians 4:4-7).
Paul exhorts us to rejoice, rather than to continue wallow in the despair of our sin and guilt. Our sin has been atoned for, and our guilt has been taken away. That is a great reason to rejoice. When we keep this fact foremost in our minds we can't help but be joyful.
In the Passion story scripture shows us two kinds of remorse. The kind that Judas had, and the kind that Peter had. Both Judas and Peter committed sin by betraying Jesus. Judas took money to sell out Jesus to the corrupt authorities. Peter, when faced with the prospect of either confessing Jesus before men and possibly suffering the same gruesome fate as Jesus, or denying Him and getting to live another day, Peter chose the latter.
Scripture tells us that they both felt remorse. Judas felt bad for what he had done to Jesus. His answer was to try to make it right. He went back to the temple, told the Pharisees that he had betrayed innocent blood, and tried to give the money back. Of course, having served their ends, the Pharisees had no further use for Judas, so they dismissed his confession and sent him on his way. Judas even threw the money back into the temple, but he wasn't able to undo the sin he had committed. In the end, the wages of his sin manifested as death by his own hand.
Peter, after he denied Jesus three times and the rooster crowed also recognized that he was guilty of a terrible sin. After all, Jesus did say that if we denied Him before men, He would deny us before the Father. That is precisely what Peter had done. He certainly recognized the state that he was in because scripture tells us that, after his denial, Peter went out and wept bitterly.
Both Judas and Peter were disciples of Jesus. Both men fell away from faith as Jesus foretold. Yet Peter was restored to faith, and Judas was lost. Why? What was the difference between the two situations?
In a nutshell, Peter repented of his sin. Judas may have felt badly for doing the terrible thing that he did, but he did not repent.
Repentance has two parts: Contrition and faith. Both Peter and Judas had the first part of repentance. They both felt sorry for what they had done. But only Peter would wind up having faith that his sin was atoned for by the blood of Jesus. Judas tired to make up for what he had done. Going back to the temple, you might say that Judas went to the Law looking for forgiveness. But the law doesn't offer forgiveness. It only condemns. It's first and primary purpose is to show us our sin, and therefore our need for a redeemer. That is certainly what happened to Judas. When he confessed his sin to the Pharisees, Judas got a sharp rebuke in return. "What is that to us?" they said. All the weight of Judas' guilt was brought to bear on him by this declaration of the law. He was responsible for what he had done; no one else on earth could take that away. And the law certainly did it's job on Judas. Instead of turning in faith to the one who could forgive his sin, however, he instead took his own life.
Peter showed his contrition as he wept bitter tears following his betrayal of Jesus. But Peter also has faith. He remains with the other disciples. They still gather together in the upper room following Jesus' crucifixion. And, when he goes to the tomb on Easter morning, he sees and believes. He knows that Jesus is the Son of God, the Lamb of God who takes away the sin of the world. And when Jesus comes to him and asks Peter three times if Peter loves Him, Peter says yes. He doesn't make excuses. He confesses his faith.
This is the difference between Peter and Judas: Repentance.
So, feel sorry for your sins, but also believe the good news of the Gospel. Believe that Jesus is the atoning sacrifice for our sins, and not only for ours but also for the sins of the whole world.
And there may be temporal consequences for our sin. That is something we must deal with. When we sin we hurt others. The result of that may be broken relationships, loss of credibility and trust, loss of our vocation, or any number of other things. Accepting and living with the temporal consequences of our sin may not be easy. It is certainly suffering. Jesus did promise us that, in this world we would have trouble.
Continue to trust in Christ for the forgiveness of sins and life everlasting, even in the face of temporal consequences for sin.
Our circumstances in this world do not determine our salvaion. Jesus also said that we should take heart, because He has overcome the world. Our feelings of sadness over the terrible things we may have done don't cancel out what Jesus has done to rescue us from sin, death, and the devil. That's why we don't fear the one who can merely kill the body. We fear Him who can destroy both body and soul in hell, because He is the one who, for the joy set before Him, endured the cross, scorning its shame, and sat down at right hand of the throne of God.
Confess your sin and do it without holding back. Ask God to also reveal anything that needs to be confessed that you may not realize or remember. If it is possible, make restitution following the example of Zacchaeus (Luke 19:8). This restitution is not penance to earn God's favor, but rather an example of bearing fruit in keeping with repentance (Luke 3:9). (Got Questions, 2006) God forgives our sin because of our faith in Jesus, and for no other reason.
If you continue to feel guilt even after confession and restitution, it is natural. We feel guilty for our sin because we are indeed guilty. However, Satan's job is to be our accuser. Don't allow him to drag you into despair. Christ has made us into a new creation. (Got Questions, 2006) And if your sin is exposed and the whole world hates and shuns you because of it, don't forget that you who are baptized into Christ are baptized into His death and resurrection. He no longer remembers our sins. They are blotted out. We are washed clean by the waters of baptism and clothed with Christ.
GotQuestions.org. How should a Christian deal with feelings of guilt regarding past sins?" August 5, 2006. https://www.gotquestions.org/guilt-dealing.html