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This week, Moshe Rabeinu (Moses) in one of his last speeches to Am Yisrael (the People of Israel) refers to "this mitzvah (commandment)" and says that it's not far away, up in the sky or over the seas, but is in Am Yisrael's hearts to do.

What mitzvah is Moshe Rabeinu talking about? Further, when reading the psukim (verses), it raises the contrast to when Am Yisrael received the Torah, and they said the famous "נעשה ונשמע," "We shall do and (only then) we shall listen."

It seems that here Moshe is describing the exact opposite situation - where Am Yisrael will complain they need someone to go bring it to them and explain it all, and only then they will do it.

What happened to Am Yisrael? Why is Moshe describing such an opposite attitude?