The Catholic Catechism of the Catholic Church in paragraph 1864 sites Mark 3:29 and then explains that the mercy of God has no limits save hardness of heart which ultimately does not acknowledge sin and thus need for repentance. This is a rejection of salvation and a direct sin against the Holy Spirit. It says:
“Therefore I tell you, every sin and blasphemy will be forgiven men, but the blasphemy against the Spirit will not be forgiven.” There are no limits to the mercy of God, but anyone who deliberately refuses to accept his mercy by repenting, rejects the forgiveness of his sins and the salvation offered by the Holy Spirit. Such hardness of heart can lead to final impenitence and eternal loss.
Traditionally, six sins are attributed to sinning against the Holy Spirit. They include:
- Despair of one’s salvation (of God’s mercy)
- Presumption of saving oneself without merit
- Resisting the known truth
- Envy of the graces received by others
- Obstinacy in one’s sins
- Final impenitence
May Justice guard our hearts from these sins so we may always yield to the gift of the Holy Spirit.
Lord, send your Spirit of Repentance that we may be transformed into the image of your love.
 Mt 12:31; cf. Mk 3:29; Lk 12:10.
 Cf. John Paul II, DeV 46.