A midrash says:
The Torah was given openly, in a public place. For if it were given in Eretz Yisrael, they could say to the nations of the world: You have no portion in it. But it was given openly, in a public place, and all who want to take it may come and take it וכל הרוצה לקבל יבא ויקבל. [Mekhilta d'Rabbi Yishmael 19:2:7; emphasis mine]
This seems to imply that the Torah belongs to all mankind, not only to study but also to observe. But, in an opinion that was accepted as halacha, the Talmud says that gentiles may study (and generally observe) only the parts of the Torah that pertain to their own seven Noahide laws, not the rest. [Sanhedrin 59a, Bava Kama 38a]
How is this apparent contradiction resolved? By saying that the Mekhilta means that Judaism is open to converts? Is this discussed anywhere?