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.
Penance
Essential to the sacrament are acts both by the sinner (examination of conscience, contrition with a determination not to sin again, confession to a priest, and performance of some act to repair the damage caused by sin) and by the priest (determination of the act of reparation to be performed and absolution). among the penitent's acts contrition holds first place. Serious sins (mortal sins) must be confessed within at most a year and always before receiving Holy Communion, while confession of venial sins also is recommended.