Ramban on Toldot: Did the Avot Keep the Torah?

God promises to Yitzhak and give the Land to his descendants because Avraham kept God's commandments. - The Torah does not use only one word, but rather says that Avraham kept God's "mishmeret", "mitzvot", "chukim", and "torot." What does all this mean? Some commentators explain that the forefathers kept the entire Torah before it was given, but Ramban points out various actions of the forefathers which would have violated some commandments in the Torah. Ramban explains that they kept the entire Torah, but only in the Land of Israel, where there is intrinsic value in keeping the mitzvot even when they are not yet officially binding commandments.