*spoiler*
Stanford wanted Stanley to hide a book, not destroy it. When Stanley went to destroy it, they got in a fight and Stanford fell through the portal. After he fell through the portal, Stanley lost the only bit of family he had left. By bringing his brother back, he'd have his family back.
Man, Stanford better realize this because I don't want any of their brotherly arguments and anger influencing Dipper and Mabel. The cinnamon buns must be protected.
Stanford wanted Stanley to hide a book, not destroy it. When Stanley went to destroy it, they got in a fight and Stanford fell through the portal. After he fell through the portal, Stanley lost the only bit of family he had left. By bringing his brother back, he'd have his family back.