The Bible certainly teaches there is an unpardonable sin of blaspheming the Holy Spirit. But fearful thoughts of whether you have committed this sin are designed by the devil to keep you out of fellowship with God. Think about it: if you’re concerned about having committed the unpardonable sin, you’re proving by your concern you have not!
But what about others? Time spent trying to judge whether another has committed the unpardonable sin removes you from the proper place of love and intercession for that person.
Jesus did mention an unpardonable sin of blasphemy against the Holy Spirit (Matthew 12:31-32). The following commentary taken from the Life Application Study Bible published by Zondervan provides good insight into the subject:
“The Pharisees had blasphemed against the Spirit by attributing the power by which Christ did miracles to Satan (12:24) instead of the Holy Spirit. The unpardonable sin is the deliberate refusal to acknowledge God’s power in Christ. It indicates a deliberate and irreversible hardness of heart. Sometimes believers worry that they have accidentally committed this unforgivable sin. But only those who have turned their backs on God and rejected all faith have any need to worry. Jesus said they can’t be forgiven—not because their sin is worse than any other, but because they will never ask for forgiveness. Whoever rejects the prompting of the Holy Spirit removes him or herself from the only force that can lead him or her to repentance and restoration to God.”
God is not trying to keep anyone out of heaven (John 3:16). Jesus’ blood paid the price for all of man’s sin; therefore, it is not individual sins that send a person to hell, but the rejection of Jesus and the work of redemption He did for us on the cross.