ISB ~ Mark 3 v29

an eternal sin:The scribes utter blasphemy by attributing to Satan what is actually the work of the Holy Spirit (3:22, 30). Their sin is not unforgivable in principle since no sin can place us beyond the reach of God’s mercy. However, blasphemy against the Holy Spirit is a form of rebellion that is particularly grievous because it blinds people to their own need for forgiveness; in this case, sins are unpardonable when they are not confessed with contrition (CCC 1864).

• The sin against the Holy Spirit was prefigured in the OT when the Israelites fashioned the golden calf (Ex 32:1-6). Instead of giving worship and thanks to Yahweh for their deliverance, they honored as their true redeemer an idol of their own making (Ex 32:4).