Although he appears only briefly and never comes to Raveloe, William Dane is the hidden hinge of George Eliot's Silas Marner. His single act of treachery in Lantern Yard determines the shape of Silas's entire life, so that the whole story of exile, miserliness and eventual redemption flows from what William Dane does at the beginning.
He is Silas's trusted friend. In the narrow religious community of Lantern Yard, William Dane is Silas Marner's closest companion, so intimate that the brethren call them David and Jonathan. Silas admires and confides in him completely, which makes the coming betrayal all the more devastating.
He frames Silas for theft. When the dying deacon's money disappears, suspicion falls on Silas because his pocket-knife is found by the empty cash-box. It is William Dane who has stolen the money and planted the evidence, hiding the empty bag in Silas's own dwelling to complete the frame. The trusted friend deliberately destroys the innocent man.
He exploits Silas's faith to condemn him. The congregation, refusing worldly proof, resorts to drawing lots, believing God will reveal the truth. The lots fall against Silas, and William Dane's guilt is masked by this false verdict. Silas is declared a thief, his belief in a just God is shattered, and William Dane self-righteously denounces him.
He steals Silas's betrothed. The injury goes further: Silas's engagement to Sarah is broken by the disgrace, and William Dane soon marries her himself. Thus Dane robs Silas not only of his good name and his faith but also of his intended wife and his future happiness.
He drives Silas into the exile that shapes the novel. Crushed and disillusioned, Silas leaves Lantern Yard for the strange village of Raveloe. Every later development, his lonely weaving, his obsessive hoarding of gold, the theft by Dunstan Cass, and the redeeming arrival of Eppie, grows out of this uprooting. William Dane's treachery is therefore the ultimate cause of both Silas's long spiritual death and his final rebirth.
Conclusion. William Dane affects the fortunes of Silas Marner absolutely: he betrays his friend, engineers his false conviction, destroys his faith and his engagement, and forces him into the exile from which the novel's action unfolds. A minor character in stage-time, he is a major cause in the moral scheme, the dark beginning against which Silas's eventual regeneration shines.