Maybe you heard somewhere that there is an “unpardonable sin” that even God cannot forgive, or won’t forgive. Pretty much, if you do this one bad thing, that’s it. Some, even Christians, are afraid they may have already committed this sin, whatever it is.
Where does this come from?
In Mark 3:28-30 Jesus faced a group of religious leaders who not only rejected Him as the Son of God, but claimed that the miracles He was performing were done by Satan’s power.
They rejected the witness of the Holy Spirit (John 16:8) that Jesus was the Son of God and Savior. The witness was clear, but they rejected it. Jesus said about them,
“I tell you the truth, all sin and blasphemy can be forgiven, but anyone who blasphemes the Holy Spirit will never be forgiven. This is a sin with eternal consequences.” He told them this because they were saying, “He’s possessed by an evil spirit.”
This still sounds a bit dicy. What if later one of them had their eyes opened and they repented and believed?
Then they would be forgiven, just like the apostle Paul--who at first persecuted the church. But if they persisted until death rejecting the witness of the Spirit that Jesus is the Savior and Son of God, then they have would have died rejecting the only sacrifice for their sins.
Again, the unpardonable sin is not saying or thinking something terrible about the Holy Spirit. That would simply be blasphemy--which Jesus said could be forgiven.
So the only unpardonable sin is going to the grave rejecting the witness of the Spirit, by not trusting in Christ as your Savior--because that is what the Holy Spirit “convicts” the world of being true.
But if you are already a believer, you cannot ever commit this sin. You are in Christ, permanently! Here is the promise of Jesus for you,
Truly, truly, I say to you, he who hears My word, and believes Him who sent Me, has eternal life, and does not come into judgment, but has passed out of death into life. (John 5:24)
And in John 6:37 Jesus says whoever comes to Him he will not drive away. It is not based on a feeling. In fact, the devil may try to lay false guilt and doubts on you. But stand on God’s promises!
And remember because God is infinitely greater than us, His capacity to forgive is infinitely greater than our capacity to sin.
And because he knows all our tomorrows (Psalm 139) He is not surprised by anything we do. He will never say, "Well, I didn't expect him/her to do that!"