The Church's sacraments are ordained for helping man in the spiritual life. But the spiritual life is analogous to the corporeal, since corporeal things bear a resemblance to spiritual. Now it is clear that just as generation is required for corporeal life, since thereby man receives life; and growth, whereby man is brought to maturity: so likewise food is required for the preservation of life.
Saint Thomas Aquinas, Summa Theologica, III, Q. 73, a.1