"Comfort, comfort my people, says your God. Speak tenderly to Jerusalem, and proclaim to her that her hard service has been completed, that her sin has been paid for..." Isaiah 40:1-2
"As many as I love, I rebuke and chasten; be zealous therefore and repent." Rev. 3:19
"This is the covenant I will make with the people of Israel after that time," declares the LORD. "I will put my law in their minds and write it on their hearts.... For I will forgive their wickedness and will remember their sins no more." Jer. 31:33-34
So many people think they have committed the unforgiveable sin or that they have gone to far and there is no hope for their souls that it is necessary to make a study on God's mercy. Truly, we cannot limit the mercy of God any more than we can put God in a box. It wasn't long ago that the Roman Catholic Church taught that if you committed suicide you automatically went to hell because you couldn't repent, but has since reversed itself saying this is limiting God and God decides who is forgiven, not us.
Actually, the only unforgiveable sin is "blasphemy against the Holy Spirit," as delineated in Matt. 12:31ff. In Jesus's day, the Pharisees went so far that they attributed the works Christ had done by the finger of God to the devil himself. They didn't just think it but proclaimed it verbally and impenitently to overthrow the ministry of Christ. That is a pretty hard sin to do in this day and age even though it is theoretically possible.
The point is that the person never repents and God sees this heart that we don't. Only God can judge that one has done this sin. No matter what sin you have committed, you can be forgiven if you repent! Israel had done every evil in the book but God didn't throw the book at them but told them even then He would not utterly cast them out and would forgive them (cf. Lev. 26:44). If you think you cannot be forgiven, you are already showing remorse and cannot be unredeemable or have gone too far; those people don't care and are impenitent.
We must realize that even Christians do not get away with sin though God does not punish them per se. He chastises and disciplines or even prunes them that they may learn their lesson. In faithfulness, He has afflicted us that we may gain a heart of wisdom and for our own good (Psalm 119:67,71). They rod and staff of God is meant to comfort us. It is good to be taught by God. Some need to learn the hard way, the school of hard knocks. Guilt complexes are of Satan, but conviction of sin is the job of the Holy Spirit and God performs an open and shut case and doesn't just give us a vague feeling of shame or guilt--Satan does! We all have a God-given conscience to listen to, but it can be wrong if not enlightened by the Word.
When God forgives us, He deletes the file on us and keeps no permanent file or record (Isaiah 38:17); He blots them out for His own sake (Isaiah 43:25). He has swept them away like a cloud (Isaiah 44:22). He also casts them into the depths of the sea (Micah 7:19). What God does is throw them into the sea and puts up a sign: no fishing! God can utterly forget and delete memories! If we confess the same sin over and over, we are dredging up old sins and God says, "What sin?" We cannot be forgiven too many times and even if it's the same sin. Do you want new sins? We may have an easily besetting sin that overcomes us and we need special intercession or confession. Remember, "Sin is crouching at the door and wants to destroy you and you must not let it." Gen. 4:7
He only forgives those with faith in Jesus and have repented of their sins. True repentance is without regret. (2 Cor. 7:10). That means being sorry enough to stop them. If there is no remorse, there can be no forgiveness. The Christian may sin, but he doesn’t desire to and wants to live a holy life and has made the decision to follow Christ. The point of conversion is that God changes a person from the inside out and makes them a new person willing to do God’s will.
God forbid that we should take advantage of grace and go on sinning once forgiven. That would be a sin of presumption. No believer is without sin but is at the same time justified before God and a sinner saved by grace, not his conduct. God doesn’t hold our sins against us (cf. 2 Cor. 5:19; Psalm 32:2). But only Christians have power to overcome sin and it has no dominion over us. (Romans 6:14).
In sum, when the believer sins, God doesn't hold it against them (cf. 2 Cor. 5:19) but disciplines them that they may grow spiritually and in maturity and faith. "O what joy for those whose record has been cleared of guilt...." (Psalm 32:2). Confession is not a matter of getting saved again, but of restoration to fellowship with the Father, the Son, and other believers as 1 John 1:9 says, "If we confess our sins, He is faithful and just to forgive us our sins, and to cleanse us of all unrighteousness." Soli Deo Gloria!