Question

Hello.

I saw in one of the Rabbi's lectures in the series "Jewish Law and Reality" that one can argue with a Jew who does not believe, asking why he desecrates the Sabbath, because halakhic facts can obligate even a Jew who does not believe. The Rabbi said in another lecture that someone who does not believe in God and the commandments—even if he performs a commandment, puts on tefillin, or joins a prayer quorum—it is not considered that he has fulfilled it. So if, from the standpoint of the commandment, he cannot fulfill it because he does not believe in it, how can one still demand of him that he observe certain commandments (for example, not desecrate the Sabbath)?
Thank you.