Why God Told Moses to Gather Seventy Elders of Israel

[(Numbers 11:16:) "GATHER ME <seventy men from the elders of Israel>."] This is what Scripture says (Amos 9:6): "He who builds His upper chambers in the heavens, and has founded His vault (aguddah) upon the earth." To what is the matter comparable? To a palace that was built upon boats: as long as the boats are joined together, the palace that is upon them stands. So too, "He who builds His upper chambers in the heavens, etc." As it were, when is His throne established on high? At the time when Israel is made into one band (aguddah). Therefore it is said, "He who builds His upper chambers in the heavens." When? At the time when "He has founded His vault upon the earth." And so it says (Deuteronomy 33:5): "And He became King in Jeshurun when the heads of the people gathered, the tribes of Israel together." Therefore the Holy One, blessed be He, said to Moses, "Gather Me seventy men from the elders of Israel." Why? Because the gathering of the righteous is a pleasure to them and a pleasure to the world, but the gathering of the wicked is a stumbling block to them and a stumbling block to the world.