something, such as wealth, that is pursued as if it were the object of worship; something that is greatly honored or revered
—Too many people chase after the golden calf of riches, only to find that it doesn’t make them truly happy.

While receiving the Ten Commandments, Moses was on Mt. Sinai for 40 days. This seemed too long for the Israelites, and they gave up on Moses and God:

When the people saw that Moses delayed in coming down from the mountain, they gathered around Aaron and said to him, “Get up, make us gods that will go before us. As for this fellow Moses, the man who brought us up from the land of Egypt, we do not know what has become of him!”

So Aaron said to them, “Break off the gold earrings that are on the ears of your wives, your sons, and your daughters, and bring them to me.” So all the people broke off the gold earrings that were on their ears and brought them to Aaron. He accepted the gold from them, fashioned it with an engraving tool, and made a molten calf. Then they said, “These are your gods, O Israel, who brought you up out of Egypt.” (Exodus 32:1-4)

Today, to “worship the golden calf” or “bow down to the golden calf” is to love money so much that one abandon’s his principles and chases after it.

God told Moses to go down from the mountain and said,

I have seen this people. Look what a stiff-necked  [stiffnecked—KJV] people they are! So now, leave me alone so that my anger can burn against them and I can destroy them, and I will make from you a great nation (Exodus 32:9,10)

Moses pleaded with God on behalf of the people, and God decided spare them.

Having a stiff neck means to be rebellious, proud, or stubborn. A stiff-necked person is like a horse that goes its own way, not willing to point its head in the right direction when it’s rider wants it to turn. Having this kind of a stiff neck is similar to having a “hard heart,” another phrase found in the Bible. God later told the Israelites:

I will give you a new heart, and I will put a new spirit within you. I will remove the heart of stone from your body and give you a heart of flesh. (Ezekiel 36:26)

The modern meaning of heart of stone is “to no sympathy or compassion for others.”

When Moses came down from the mountain and saw the Israelites worshipping the idol they had made, he became so angry that he threw down the stone tablets containing the Ten Commandments, breaking them. Even though God had chosen not to destroy all the people, as punishment, he did have about 3,000 of them killed and punished the rest of the people with a disease. Moses then went back up the mountain, where God gave him a new copy of the Ten Commandments.