You shall not make for yourself an image in the form of anything in heaven above or on the earth beneath or in the waters below. You shall not bow down to them or worship them; for I, the Lord your God, am a jealous God, punishing the children for the sin of the parents to the third and fourth generation of those who hate me, but showing love to a thousand generations of those who love me and keep my commandments.
You shall not make for yourself an idol in heaven, on earth, or under the earth. There is to be no idol made to anything. This made Israel separate from other nations around them. Everybody made and worshipped idols. When Moses was up on the mountain for a long time, what did the people tell Aaron to do? Make an idol. And he did it. Why? This is what people know. This is what you did. People made idols.
But making and worshipping idols replaces the sole worship and devotion to YHWH with devotion to multiple things. Even if people made an idol to YHWH, that would reduce YHWH to something controlled by humans. YHWH is supposed to rule the people, not the other way around. They are to put their whole faith and devotion into their worship of YHWH, and to do so means to quit making idols. Do not shrink God down to the size of an idol, but worship him as he is.
God is holy, mighty, powerful, and worthy of our praise. Don't replace your worship of God with worship of something else, and don't shrink God down to the size of an idol.