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 theology
In Russian variant of Eastern Christianity, sin sometimes is regarded as any mistake made by people in their life. From this point of view every person is sinful because every person makes mistakes during his life. When person accuses others in sins he always must remember that he is also sinner and so he must have mercy for others remembering that God is also merciful to him and to all humanity.