Impeccability is an inability to sin, while sinlessness refers to an absence of actual sin. The Abrahamic religions teach impeccability to be an attribute of God. Logically God cannot sin: it would mean that God would act against God's own will and nature. Impeccability is therefore also attributed to Jesus Christ in Christianity. The Letter to the Hebrews asserts that Christ "did not sin". Islam further teaches a concept of 'iṣmat al-anbiyā, the sinlessness or impeccability of prophets, which has been compared to Papal infallibility in early Catholic doctrine.

In the New Testament, the Letter to the Hebrews asserts that Jesus Christ "did not sin".

The writer of the apocryphal Prayer of Manasseh states that Abraham, Isaac and Jacob did not sin against God.

The Roman Catholic Church teaches that Mary, mother of Jesus was, by a special grace of God, without sin throughout her life. This included the moment of her conception, so Mary was even miraculously preserved from original sin and its effects. Some theologians have asserted this special grace extended to impeccability (understood in this context as the inability to sin); others argue this could not be so: as a natural human being, she would have had free will and therefore the ability to sin but through her cooperation avoided it.

Impeccability is sometimes confused with infallibility, especially in discussions of papal infallibility. Impeccability is an attribute not claimed by the pope, and few would deny that there have been bad popes: Saint Peter himself denied Jesus three times. On the other hand, Pope Gregory VII, intellectual progenitor of the Ultramontanes and nemesis of the lay faction in the investiture controversy, voiced an assertion of papal prerogative beyond even the strongest of modern apologists:

The pope can be judged by no one; the Roman church has never erred and never will err till the end of time; the Roman church was founded by Christ alone; the pope alone can depose and restore bishops; he alone can make new laws, set up new bishoprics and divide old ones. ... He alone can call general councils and authorize canon laws; his legates ... have precedence over all bishops. ... A duly ordained pope is undoubtedly made a saint by the merits of St. Peter.

Nevertheless, in Catholic thought, the exemption of the See of Rome from all error extends only to its definitive teachings on faith and morals, not to its historical judgments. Similarly, papal sainthood does not suggest that popes are free from sin. Quite the contrary, popes frequent the sacrament of Reconciliation (confession and penance) for the forgiveness of their sins, as all Catholics are required to do. While occupying the papal office, Pope Benedict XVI confessed his sins weekly.

Early Christians questioned whether the victorious saints in heaven could sin. Church Father and theologian Origen of Alexandria maintained that they could; official Roman Catholic doctrine holds that they cannot. Although Catholics believe in the gift of free will, saints in heaven already see God face to face and are incapable of sinning (see Pope Benedict XII and beatific vision), i.e., they will necessarily remain in God. The Catechism of the Catholic Church states (emphasis added):