Nedarim 38 - Only Moses had to observe the Torah
Rabbi Yose the son of Rabbi Chanina said, "The Torah was given only to Moses and his descendants," because it clearly states " Carve for yourself " and " Write for yourself ." However, Moses was nice and gave it to all Israel.
Now, how could it be? Aren't all Israel obligated to fulfill the Torah? Moses himself said, " I was commanded by God at this time to teach you the laws and statutes ." - Sure, Moses was commanded, he alone, but he chose to teach to all.
But what about the song which Moses wrote so that " it will be for God a testimony ?" If they were not commanded to keep the Torah, what testimony is needed?
The Talmud concedes the point and gives the following explanation: of course the Torah was given to all Israel. Only Moses and his descendants, however, were initially given the power for logical analysis and deductions. Out of the goodness of his heart, he taught this to all.
Art: Moses with the Ten Commandments by Philippe de Champaigne