Why do we have to do all this stuff?

"Speak unto the children of Israel" (Leviticus 1:2).
Rabbi Avin said: A parable about a king, who had purple cloaks and would command his servant, saying to him: Pay attention to this one and fold it and shake it. He said to him: My master the King! Of all the purple cloaks that you have, you have only commanded me about this one?! He said to him: It is the one I wore on the day I became king. Likewise, Moses said before the Holy Blessed One: Master of the Universe! Out of the 70 independent nations that You have in Your world, you have only commanded me about Israel! "Command the people of Israel" "Say to the people of Israel." [God] said to him: It is they who made me king first, when at the Sea they said to me "Adonai will rule for ever and ever" (Exodus 15).
Rabbi Berchia said: A parable about an Elder, who had a hooded cloak and would command his student, saying to him, fold it and shake it. He said to him. My master the King! Of all the hooded cloaks that you have, you have only commanded me about this one?! He said to him: Because I wore it when they appointed me Elder. Likewise said Moses before the Holy Blessed One: Master of the Universe! Out of the 70 independent nations that You created in Your world, you have only commanded me about Israel?! [God] said to him: It is because they accepted upon themselves My kingship at Sinai, saying "All that Adonai says, we will do and we will obey"(Exodus 24).