Eternal sin
Thomas Aquinas lists, or has responded to, six sins that supposedly go against the Holy Spirit:
Thomas Aquinas explains that the unforgivability of blasphemy against the Holy Spirit means that it removes the entrance to these means of salvation; however, it cannot hinder God in taking away this obstacle by way of a miracle.
Ethics in religion
Christian ethics in general has tended to stress the need for love, grace, mercy, and forgiveness because of sin. With divine assistance, the Christian is called to become increasingly virtuous in both thought and deed, see also the Evangelical counsels. Conversely, the Christian is also called to abstain from vice.