In Scripture, the sin of idolatry is not limited to the complete displacement of the true God by false gods. It also includes the worship of false gods alongside the true God. The Jezebels who wanted Baal and Asherah instead of Yahweh were certainly idolaters, but so were the average Israelites who thought of themselves primarily as Yahweh worshipers who happened to dabble in Baalism, Asherism, and any number of other “-isms” in order to cover their bases. In other words, your heart doesn’t have to be exclusively devoted to a false god in order for the act to qualify as idolatry. In fact, rarely would it be the case that pagan worship would entail the full devotion of the heart. Pagan worship, in contrast to biblically defined worship of the one true God, could best be characterized as a kind of business transaction in which the worshiper jumps through all of the right hoops in order to placate the gods and secure favors from them. It would be very easy to be an idolater while also maintaining one’s basic identity as a worshiper of Yahweh.
Consider the most common analogy for idolatry in Scripture: adultery. Can a husband commit adultery while still wanting to keep his wife? Of course he can. In fact, that is most commonly how adultery works. The husband is not seeking to replace his wife, because there are many elements of the life he has built with her that he wants to hold on to. However, in the act of adultery he demonstrates that he is seeking some (though not all) elements of marital fulfillment in another woman. He is trying to hold on to his identity as a husband while simultaneously seeking outside the marriage what he has promised to seek only within the marriage. Adultery does not require the full devotion of the heart. It merely requires a division of the heart, which then becomes pulled in different directions.
So I would define idolatry in this way: Idolatry is the sin of seeking from a creature or from an imaginary entity what we are obligated to seek only from the one true God. I think this definition fits the biblical data and shows how an Israelite who dabbled in Baalism in order to get Baal on his side, while still maintaining a formal devotion to Yahweh, would still qualify as an idolater. Under the terms of the Mosaic Covenant, Israel was to have no other gods, period. She was to be exclusively devoted to her husband. God has no interest in an open marriage.
If my definition is on target here, then I am forced to conclude that the Roman Catholic Church has become entrenched in idolatrous practices of praying to and venerating Mary and the saints. Nothing in all of Christendom is so pagan as those practices. Yes, Catholic theologians are very careful to distinguish “worship” (reserved for God alone) from “veneration,” but if what I have said above is right, that distinction is not one that preserves them from idolatry. You don’t have to go all the way and say, “I worship Mary alone” in order to qualify as an idolater. All that is required is seeking from Mary what you should be seeking from God. And I would argue that the supernatural status and godlike abilities that Catholics attribute to Mary parallels very closely the same kind of status and abilities that Israelites would have attributed to Baal, Asherah, etc. when they sought to cover their bases by “venerating” them as well.
I have great respect for the rich tradition of the Roman Catholic Church, and I anticipate that I will continue to learn from Catholic theologians and philosophers many profitable things for the rest of my life. And I do not doubt that it has been and will continue to be a major force for good in this world, an institution through which many individuals come to know God through Jesus Christ. But as long as Rome officially denounces the doctrine of justification by faith as damnable heresy (as the Council of Trent did), and as long as it promotes the idolatry of seeking from creatures such as Mary and the saints what we are biblically required to seek only from God, I am forced to conclude that it is an institution that has publicly forfeited its adherence to the gospel and thus stands in desperate need of repentance. I long for the day when reconciliation between Protestants and Catholics can occur, but these two issues–justification by faith and paganism in Roman worship practices–remain the primary barriers to making that possible.