The major theme of Old Testament is Monotheism and not to do idolatry, You can see this especially in the chapters f Deuteronomy from about chapters 4 to 10 and in the events surrounding the kings of Judah and Israel. I was reminded of this today listening to the events surrounding the anointing of Yehu. [He was anointed king in order to wipe out the house of Ahab --because they did idolatry, Not because of Jewish identity. For King Ahab was as Jewish as can be. But in the eyes of God, Jewish identity makes not the slightest bit of difference. What matters to God is only one question: did Ahab serve idols or not, Of course in those days this was an easier question to answer. Nowadays they dress idols in Jewish garments and that is supposed to make it ok.
For anything besides God can be an object of idolatry, It does not have to be a statue. It can be a person even true tzadikim. All the more so fake tzadikim. This is in fact one of the reasons for the signature on the letter of excommunication(herem). That is the reasons of idolatry.
