Final answer:
In Roman doctrine, a sinner must confess their sins to a priest to receive absolution and perform the penance given by the priest, which stems from the practice of confession in the Roman Catholic Church.
Step-by-step explanation:
According to the Roman doctrine, a sinner must confess its sin to a priest. This stems from the practice where penitents confessed their sins to the priest, who then absolved them and assigned them penance. The Roman Catholic doctrine holds that the sacrament of confession, also known as reconciliation or penance, allows individual sinners to receive forgiveness for their sins and reconcile with God and the Church, provided the sinner has true contrition and commits to perform the penance given by the priest.
The power to forgive sins is based on the belief that the priest, through ordination, acts in persona Christi, meaning 'in the person of Christ.' Therefore, in the Roman Catholic tradition, it is not merely the priest, but Christ working through the priest that forgives sins upon confession. However, teachings that suggest buying souls out of purgatory or purchasing confession privileges, which negate the necessity of contrition, are considered unchristian.