God gave her to me because you turned your back upon her, and He looks upon her as mine: you've no right to her! When a man turns a blessing from his door, it falls to them as take it in. (2.19.34)
This may seem like greed—Silas wants to keep Eppie for himself—but he understands it as just a simple law of property. Godfrey tossed Eppie out, or at least failed to take her in, and so Silas gets to keep her. In other words: finders, keepers; losers, weepers.