In parshas Shilach, (Numbers, 15:31) we find a warning stating that whoever commits idolatry “despises God’s word”. Rashi states, “the warning for idolatry is from God, all other (warnings) are from Moses.” The question is what necessity is there for God to be the One admonishing us, in this single case? Directed more towards an answer, what would be lacking in the warning of idolatry, had Moses - or better yet a man - been the one warning us, and not God?
This second formulation of the question directs us to the concept of what exactly the purpose of a “warning” is, and how in the case of idolatry alone, is God’s warning essential for being most effective.
A warning, by definition, is part of the Torah system. The Gemara asks at times, “The punishment for such and such a crime we see, but from where is the warning derived?” Meaning, the Torah system does not only state punishments for violations, but it also includes passages that serve to warn man from acting in a certain way. The reason why we have warnings, and not punishments alone is to educate man on the destruction, which prohibited actions cause to his soul. By investigating the ruin that results from such actions, man may better understand why not to engage these acts. Man will come to conquer his drive for such actions by understanding the good derived from abstention. Thereby, man comes closer to the life of reality and goodness, which is only derived from complete adherence to the Torah’s principles.
A warning, then, must carry with it some principle whereby man is not forced to abstain through fear. Man is encouraged to abstain due to his appreciation of following what is real and good. As the argument offered to abstain becomes more conclusive, man will be more convinced and his chance for abstention will be greater.
Not only is the content of an argument essential, but the delivery can also play a role. What is the best argument from abstention from idolatry? It is a warning delivered by God Himself from amidst the flames of Sinai. Such a warning against idolatry - which all the Jews heard - is the most compelling argument. If God created an event where an entire mountain is ablaze, and intelligent principles were heard from those flames; then those who witnessed this event were convinced that an intelligent Being controls the world, exclusive of impostors. Thereby, God eliminated the notion of idolatry.
Sinai was the best formulation of a warning against idolatry, and remains our Judaic proof of God’s existence.