Everyone who accepts the Seven Laws and is careful to do them, this person is one of the Chasidei Umos HaOlam (very pious of the nations of the world), and he has portion in the world to come. This applies to one who accepts them and will do them because the Kodosh Baruch Hu commanded them in the Torah, and informed us by means of Moshe Rabbenu, that Noahides were previously commanded concerning these laws. But if he does them because of an intellectual decision, then he is not a Ger Toshav, and is not of the Chasidei Umos HaOlam, he is [only] one of their Chochmei Umos HaOlam (wise men of the nations of the world).
Maimonides - Laws of Kings and their Wars, Chapter 8