St. Thomas Aquinas
“It (Eucharist) was instituted not for satisfaction, but for nourishing spiritually through union between Christ and His members, as nourishment is united with the person nourished. But because this union is the effect of charity, from the fervor of which man obtains forgiveness, not only of guilt but also of punishment, hence it is that as a consequence, and by concomitance with the chief effect, man obtains forgiveness of the punishment, not indeed of the entire punishment, but according to the measure of his devotion and fervor.”
Source: St. Thomas Aquinas, Summa Theologica