I gave a definition to be clear about what idolatry really is:
Idolatry is a very, very serious crime and a very serious sin. It comes in three forms, if you read the early church fathers: (1) worshipping physical objects made in the image of God or gods; (2) making sacrifices to pagan gods (as was required in government proceedings in the time of Rome); and (3) making offerings to the dead. Tertullian gave examples in his writings: banquets for the dead including sacrifices, blood sacrifices, burning incense, allowing yourself to be bound to a sacred priesthood not of Christ, praying to physical objects, or making such physical objects for others.
This post has been on my mind for a few months, and I wanted to give a few examples of things which are "on the borderline" and which Christians need to be very, VERY careful...for they risk violating God's command to avoid the grave sin of idolatry. Now rarely today do I see a Christian in danger of violating #2 or #3 above: very few sacrifice to pagan gods or give sacrificial offerings to the dead.
However, definition #1 (giving worship to physical objects) is still very much a danger for many Christians.
Veneration vs. Worship
Now before I can give examples, we must of course address a very technical distinction of the term "worship" used by the Orthodox and Catholics: these groups would say that "adoration" is proper worship--that is, giving honor due to God alone; yet "veneration" is giving honor and therefore is appropriate for saints and others.
I--like many ex-Catholic Protestants--find it extremely difficult to believe that anyone is able to maintain such a distinction in their minds. Take the Rosary, for example, in the Catholic Church. During this it is expected that the person switches from worship/adoration (when saying the Our Father) to veneration (when saying the Hail Mary) then back to worship, then back to veneration, etc. From a practical standpoint I can tell you that this "magical shift" in the thinking does not happen--or at least, it didn't in my experience or any other Catholic I've spoken to. Rather, all the prayers are said in the same frame of mind...thus either all are "veneration" (in which case God is lowered to the same level as Mary and the saints) or all are "adoration/worship" (in which case Mary and the saints are worshipped through idolatry and violate God's command).
Likewise, it is supposed that when you genuflect/bow before the altar or cross you do so to worship God, but when you do so at the hearing of Mary's name or before a statue, it is purely to give honor, like how a Japanese man shows respect by bowing.
I find it nearly impossible to believe that anyone is able to switch back and forth mentally so quickly between giving honor to Mary/saints and giving worship to Christ/God.
However, for the sake of argument let's assume that such a technical distinction can be made: that somehow, there is such a thing as veneration which is different from adoration/worship and the two can be separated.
Even if these can be separated, we may look at some common practice of Christians which either definitely or nearly pass the line of idolatry, applying worship to physical objects instead of God.
Definite Idolatry: Adoration of the Eucharist
I am a big fan of communion, as I have written about before: I consider it a tragedy that so many Christians have abandoned the early church call and practice to celebrate communion together every week, a reminder of Christ's sacrifice for us.
Now the Catholics, beginning in the Middle Ages, began to teach that the bread of communion literally became human flesh of Jesus, and the wine literally became blood. (But of course they still taste like bread and wine.) This doctrine, called transubstantiation, means that when the communion bread and wine have been blessed, they literally and really become part of God Himself.
As a result, it is common to worship and adore the bread and wine (see this article, for example). I cannot state strongly enough that this is idolatry. This is the very definition of idolatry. This is the worship of a physical object (bread and wine) because it is supposed to somehow be linked to God. It is entirely inappropriate and clearly outside of the scope of what any of the early Christians believed or would have approved.
There is not a scant bit of evidence in the early church fathers that such a doctrine even existed before about 1100 AD, and one cannot with any sort of open mind read the Biblical references to communion and gather any such belief. Further, one cannot read with an open mind either the Bible or any early church father and conclude that this is an acceptable practice. This practice is over the line of idolatry and aims worship which is only legitimate for God into a piece of bread and some wine. Read some of the discussions about dropping or handling the communion wafer (such as here) and you will see that this has taken on a level far beyond what is appropriate.
Borderline Idolatry: Veneration of Saints
Not to pick on the Catholics again, but they skirt the borderline (and often cross it) when it comes to venerating the saints. Theoretically, they are simply giving honor to someone who is a great example of faith and promising to follow in their footsteps. Then they also ask these people to pray for them (despite the fact that they are dead and there is no actual Biblical evidence that such post-death intercessions are possible).
So is it idolatry? Hmmm...it is close. If you can manage to only be giving honor and never be attributing to the saints a super-human status or ability, then I suppose it is probably not idolatry. But if you carry around a necklace that you hold up and pray every time that you lose something to help you find it...then yeah, that is idolatry.
My personal rule of thumb when it comes to veneration (and it was the same when I was a Catholic) is this: idolatry is one of the Big Sins when it comes to God, so you shouldn't even go anywhere near it. If I was seen as a godly man by someone around me, I would not want them giving me honor--that is due to God. (And we see that in the Bible with angels...they are always very quick to point people who look to give them honor back to pointing at God.) So why would you ask St. Anthony to pray to God to help you find something lost, when you can just pray to God directly? Not only are you going "straight to the source" as it were, but you are eliminating any risk of committing idolatry.
So for me, you should not venerate saints because you are running a serious risk of being idolatrous. And the Catholic Church itself recognizes this as a serious problem, condemning those who transfer feelings about God to statues, for example (Second Nicaea, Council of Trent, CCC 2114). So the question is...why run such a serious risk?
Borderline Idolatry: Veneration of the Bible
I'm not just going to pick on Catholics here...time for my fellow Protestants to take a turn in the barrel.
As I have written before, many Protestants worship the "Father, Son, and Holy Scripture" instead of the "Father, Son, and Holy Spirit." We should honor the reading of God's word. The Scriptures are divinely inspired and handed down to us carefully through the ages. They are a significant aid to our faith and serve a valuable role for helping us understand the teachings of Jesus and His apostles.
BUT...the scriptures are not the center of our faith. Jesus is. The scriptures are the word of God, while Jesus is the Word of God. The capitalization is subtle, but important.
There are many Christians who are known to open the Bible at random and seek the answers to their burning questions on whatever page they land. There are many Christians who quote Scripture massively out of context and then build theology around it. There are many Christians who see the Bible as a tool to justify their politics or lifestyle rather than as a history of our faith and doctrine. There are many Christians who see the Bible as a book with the answers for every issue in life, rather than the book that points to the One who has the answer for every issue in life.
And when they do so--when they treat the Bible like a Ouija board, when they treat the Bible as though it has the answers rather than as a sign pointing to the One with the answers--then they cross the line into idolatry.
Ironically, there are many Protestants who cry "Idolatry!" to the Catholics worshipping saints...and yet they themselves worship the writings of these saints.
Remember, don't worship the Bible. It is a book. It's a book of more value than every other book ever written added together...but it's still a book. It contains the divine wisdom of God written down for our benefit...but it's still a book. It is not God. Do not let it become your god, or you are no better than those who worship the saints.
Idolatry is a big deal. A big, big deal. Take it seriously. The only object which is appropriate for your worship is the Triune God--Father, Son, and Spirit. Never forget this.