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.
Christian denomination
Christianity has not been a monolithic faith since the first century or Apostolic Age, if ever, and today there exist a large variety of groups that share a common history and tradition within and without mainstream Christianity. Christianity is the largest religion in the world (making up approximately one-third of the population) and the various divisions have commonalities and differences in tradition, theology, church government, doctrine, and language.