Among the sins to which the human heart is prone, hardly any other is more hateful to God than idolatry, for idolatry is at bottom a libel on His character. The idolatrous heart assumes that God is other than He is – in itself a monstrous sin – and substitutes for the true God one made after its own likeness…Let us beware lest we in our pride accept the erroneous notion that idolatry consists only in kneeling before visible objects of adoration, and that civilized peoples are therefore free from it. The essence of idolatry is the entertainment of thoughts about God that are unworthy of Him. It begins in the mind and may be present where no overt act of worship has taken place…Wrong ideas about God are not only the fountain from which the polluted waters of idolatry flow they are themselves idolatrous. The idolater simply imagines things about God and acts as if they were true.
— A.W. Tozer, Knowledge of the Holy (pp 3,4)