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.
Seven deadly sins
With Christianity, historic Christian denominations such as the Catholic Church and Protestant Churches, including the Lutheran Church, recognize seven virtues, which correspond inversely to each of the seven deadly sins. 
Confession is the act of admitting the commission of a sin to a priest, who in turn will forgive the person in the name (in the person) of Christ, give a penance to (partially) make up for the offense, and advise the person on what he or she should do afterwards.