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.
Jewish views on sin
Sins between people are considered much more severe in Judaism than sins between man and God. Yom Kippur, the main day of repent in Judaism can atones for Sins between man and God, but not for Sins between man and his fellow, that is until he has appeased his friend.(Mishnah, Yoma,8:9). Eleazar ben Azariah derived [this from the verse]: "From all your sins before God you shall be cleansed" (Book of Leviticus,16:30) – for sins between man and God Yom Kippur atones, but for sins between man and his fellow Yom Kippur does not atone until he appeases his fellow.