-Vindicated Before G-d and Before People

"Vindicated Before G-d and Before People"

In parashat Matot, when the tribes of Reuben and Gad (and later half of Menashe) decided to stay on the eastern side of the Jordan, Moses suspected rebellion on the part of the people and feared that it may lead to tragedy. When Moses is convinced that the tribes intend to do their share in the battle against the Canaanites, he agrees to let them stay on the eastern side of the Jordan. Moses tells the tribes that if they do their share in the battle, "they will be vindicated before G-d and before Israel." What does this notion of vindication mean?