Catechism of the Catholic Church
1864 - "Therefore I tell you, every sin and blasphemy will be forgiven men, but the blasphemy against the Spirit will not be forgiven."136 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.137 Such hardness of heart can lead to final impenitence and eternal loss.
136 Mt 12:31; cf. Mk 3:29; Lk 12:10.
137 Cf. John Paul II, DeV 46.