Presumption.
Presuming God's forgiveness/mercy.
Which is a sin in itself.
Presumption.
From newadvent.org:
Presumption
(Lat. praesumere, "to take before", "to take for granted").
Presumption is here considered as a vice opposed to the theological virtue of hope. It may also be regarded as a product of pride. It may be defined as the condition of a soul which, because of a badly regulated reliance on God's mercy and power, hopes for salvation without doing anything to deserve it, or for pardon of his sins without repenting of them. Presumption is said to offend against hope by excess, as despair by defect. It will be obvious, however, to one who ponders what is meant by hope, that this statement is not exact. There is only a certain analogy which justifies it. As a matter of fact we could not hope too much, assuming that it is really the supernatural habit which is in question.
In the Vedas this sin is called "nama bale papa buddhi" - knowingly commiting sin on the strength of the holy Name of God. If someone thinks "I am saved because I take shelter of the all purifying Name of God, therefore I can sin any way I like and I'll be cleansed", they are NOT purified even by the all-purfying Name of God, and thus pave their way to hellish life after death.
The main difference between Vedic religion (the original source of Hinduism) and Christianity is that hell is not permanent. It may be similiar to the Catholic description of Purgatory, except the Vedic descriptions of hells (there are many) are very severely terrible. But after a long, long time the soul is given another chance.