What is the unforgivable sin? This sermon on Mark 3:20-35 is an attempt to answer that question from the context of the passage. While there have been a wide range of interpretations of this Scripture, context is king in understanding this.
This passage is closely related to Hebrews 6:4-6. The issue is how people respond to the illumination of the Holy Spirit. If they respond by rejecting that illumination (not regeneration, which cannot be rejected any more than a baby can choose to reject life when it is born by an act of its will) and then crediting the truth they have learned to the work of Satan himself, they have committed the unpardonable sin. Or, as Jesus puts it in this text, an eternal sin (ESV).
There is much more here than just the unforgivable sin. There are statements on reality with Jesus, the meaning and extent of forgiveness of sins, and more. I hope you will take the time to check it out.