“You shall not make for yourself a carved image—any likeness of anything that is in heaven above, or that is in the earth beneath, or that is in the water under the earth; you shall not bow down to them nor serve them. For I, the Lord your God, am a jealous God, visiting the iniquity of the fathers upon the children to the third and fourth generations of those who hate Me" Exodus 20:4.
Why would God create such a commandment? This is because the Jews were His, and because He loves them.
Claiming someone to be your God means that you're calling them the Creator of everything, so claiming a false idol/god means that you're kicking God out of His rightful place.
When the Jews made the golden calf out of the gold that they had, they were making an idol and kicking God out of His rightful place. This grieved God so much, but they were only showing their heart. They were willing to look anywhere but to God for their needs, but God had just taken them out of slavery and provided for them in the desert. Their clothes hadn't aged, and their shoes didn't wear out while walking in the desert. This is the type of miracle that God did for them, but they still complained.
Are you complaining to God, or are you looking to Him for your daily needs?