Truly I tell you, people can be forgiven all their sins and every slander they utter, but whoever blasphemes against the Holy Spirit will never be forgiven; they are guilty of an eternal sin.” Mark 3:28-29

            God can forgive any sin except the sin of rejecting God.  The Holy Spirit’s job is to convict people of their sins.  Blaspheming means to reject God.  If you reject the Holy Spirit, you reject the conviction of your sin and decide to remain in your sins.  That is not a one-time sin, but an ongoing issue.  In the end, when you die, your rejection of conviction will lead to a conviction, for eternity.  You won’t be forgiven after your sentencing and you will spend eternity separated from God paying for your sin.