מוסר אויף שמות 32:9

However it is not only the trait of ingratitude that is the root of heresy and of all the destructive actions. Rather, it is all of the [bad] character traits. And even at the time when the Jewish people sinned with idolatry, they were only prosecuted on account of [their] defective character traits: We have seen with the sin of the calf that God said about it to Moshe (Exodus 32:8), "they have made for themselves a molten calf, and have prostrated themselves to it and offered sacrifices to it." Nevertheless, when He came to punish them, it is written (Exodus 32:9), "And the Lord said to Moshe, 'I have seen this people, and behold they are a stiff-necked people.'" Note surely that the main sin of idolatry is not in the actual idolatry, but rather in the character trait that brought it into motion.