The proverb one reaps what one sows is the moral backbone of George Eliot's Silas Marner. Eliot structures the novel so that every character's harvest, good or bad, grows directly from the seed of his earlier conduct.
Godfrey Cass sows deceit and reaps childlessness. Godfrey secretly marries Molly Farren, then hides the marriage and denies his own daughter to protect his inheritance and marry Nancy Lammeter. He sows cowardice and concealment. His harvest is a long marriage without children of his own, for Nancy bears him none. When at last he confesses and comes to claim Eppie, she chooses Silas, and Godfrey reaps the very emptiness his early lie planted.
Dunstan Cass sows theft and reaps death. Dunstan steals Silas's gold and disappears. For sixteen years his crime seems unpunished, but he had fallen into the Stone-pit that same night and drowned. When the pit is drained his skeleton is found beside the stolen gold. His secret sin yields a secret, wretched death.
Silas sows patient love and reaps joy. Robbed and embittered, Silas nevertheless opens his heart to the golden-haired child who wanders into his cottage on the night his gold vanishes. He sows years of tender, self-denying care for Eppie. His harvest is her devoted love, which enriches his old age far beyond the gold he lost, and even the stolen money is finally returned.
Eppie reaps the security of honest affection, choosing the poor father who nurtured her over the rich one who abandoned her.
Through these interlocking fates Eliot demonstrates a firm moral law: selfish deceit and greed ripen into loss and death, while patience, honesty and love ripen into happiness. What each character reaps is exactly what each has sown.