So Jesus used this illustration: "If you had one hundred sheep, and one of them strayed away and was lost in the wilderness, wouldn't you leave the ninety-nine others to go and search for the lost one until you found it? And then you would joyfully carry it home on your shoulders. When you arrived, you would call together your friends and neighbors to rejoice with you because your lost sheep was found. In the same way, heaven will be happier over one lost sinner who returns to God than over ninety-nine others who are righteous and haven't strayed away! (NLT, Luke 15:3-7)
When we have sinned, we can ask God for forgiveness, as in the Lord's Prayer:
and forgive us our sins, just as we have forgiven those who have sinned against us. (TLB, Matthew 6:12)
Related verses: Psalms 25:7, Psalms 32:1-2, Isaiah 43:25, Matthew 1:21, Matthew 18:12-14, Matthew 26:28, Luke 15:11-32, Acts 10:43, Acts 13:38, Romans 4:7-8, Hebrews 10:17.
From that time on Jesus began to preach, "Repent, for the kingdom of heaven is near." (NIV, Matthew 4:17)
True repentance involves sorrow for acts of sin and leads to a fundamental change in attitude. We are all sinners in our own ways (Romans 3:23, 1 John 1:8), and we may fail time and again in our attempt to avoid sin. God is always willing for us to start over and make another attempt. However, if we ask for forgiveness with the intention of sinning again, we have not really repented.
Related verses: Matthew 3:2, Matthew 4:17, Mark 1:15, Mark 6:12, Luke 3:3, Luke 5:31-32, Luke 13:3-5, Luke 24:47, Acts 2:38, Acts 3:19, Acts 8:22, Acts 17:30-31, Acts 20:21, 2 Corinthians 7:10.
If you forgive those who sin against you, your heavenly Father will forgive you. But if you refuse to forgive others, your Father will not forgive your sins. (NLT, Matthew 6:14-15)
Forgiving another person means pardoning the offender and ceasing to feel resentment or hold a grudge. We are not able to completely forget what happened, but we must let go of the anger and resentment.
There should be no limit to our willingness to forgive others (Matthew 18:21-22). We should have a forgiving spirit whenever someone has committed an offense against us (Mark 11:25). Some people believe there is no obligation to forgive unless the offender repents, but that condition is mentioned in only one of the many passages on this topic (Luke 17:3-4). Continued anger and holding a grudge are always wrong (Matthew 5:21-24). Holding a grudge turns a person bitter and blocks the love of God.
Forgiving others does not mean we are required to remain in an abusive or exploitive situation. Neither does it deny the right of governments to punish offenders. Jesus and other New Testament leaders supported the authority of civil governments (Matthew 22:15-22, Romans 13:1-7).
Related verses: Matthew 6:12, 18:23-35, 5:43-47, Luke 6:37, Ephesians 4:32, Colossians 3:13
However, some Christian counselors warn that we must use wisdom in deciding when and how to confess secret sins. We must consider how the other person will react and whether good or evil will result. For example, confessing a romantic infatuation to a jealous spouse could lead to the greater evils of divorce and emotional damage to the children.
The New Testament does not specifically state that making restitution, making amends or otherwise correcting the wrong done are requirements for forgiveness. However, doing what is possible to correct the wrong done could be an important part of sincere repentance (Luke 19:2-10).
I tell you the truth, all the sins and blasphemies of men will be forgiven them. But whoever blasphemes against the Holy Spirit will never be forgiven; he is guilty of an eternal sin. (NIV, Mark 3:28-29)
The nature of this sin has been the subject of much debate. In context, Jesus was referring specifically to the sin of the scribes (teachers of the law) (Mark 3:22-30) who said Jesus was possessed by demons and had an evil spirit. The total spiritual blindness of those who mistook the work of Jesus for the work of Satan put them beyond hope of repentance, faith and forgiveness.
Some people worry about committing the unpardonable sin accidentally or in a moment of weakness, but most Bible experts say there is no need for such worry. It is not that any sin is beyond the power of God's grace. The sin of the scribes was not forgiven because their own stubborn perversion of the truth and hardness of heart prevented them from repenting. Those people who are concerned enough to worry about their sins are not in danger of committing an unpardonable sin.
Related verses: Matthew 12:31-32; Luke 12:10.
In their original context, these were warnings, in the strongest possible terms, to the first century Christians not to abandon their new faith because of persecution or false teachings. Thus, the authors may have used some hyperbole (exaggeration) to emphasize the point. [Jesus also sometimes used hyperbole for emphasis (Matthew 7:3-5, Mark 10:25).]
If these verses really mean that a person who has fallen away has no chance to repent, that would seem to contradict many other New Testament teachings about God's mercy and constant willingness to forgive. These verses are probably not directed at people who have doubts or who lose their faith and come back later. It is the person who deliberately, permanently and hard-heartedly rejects faith who will never repent, and thus can never be forgiven.
Related article: What Does the Bible Say About Faith?