Nedarim 38 - Only Moses had to observe the Torah
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 Moses wrote so that "it will be for God a testimony?" What testimony is needed if they were not commanded to keep the Torah?
The Talmud concedes the point and explains that the Torah was given to all of Israel. However, only Moses and his descendants 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
