Excerpt from LOF series #3 (
http://bible-truths.com/lake3.html):
And so we are assured that EVERYONE will be "revealed," "tried," "salted," and "baptized" "in FIRE." And these fiery trials as Peter calls them go on for a lifetime. If it were real, physical fire, all believers’ lives would be short indeed. God is SPIRIT, and God is a CONSUMING FIRE. It is God’s SPIRIT that is likened to fire. The spiritual teaching in this symbol is to recognize what real fire accomplishes and to then use that as an analogy as to what God DOES TO US (or more properly FOR US).
Fire does a number of things:
1. Fire CHANGES things. Fire brings about molecular changes in the materials that are burned. God’s spiritual fire will make changes in our mind, heart, and spirit.
2. Fire PURGES. In times past if a building were diseased and rat-infested, they would purge away the filth by burning it down. We are to be purged from all our diseases of sin and carnality. Jesus Christ paid the penalty of sin for us, but now God wants to get at the root and core of what caused us to sin in the first place. We all need desperately to be CHANGED and PURGED.
3. Fire BURNS UP combustible materials that have no value in saving. God will burn out of all of us the straw, grass, and stubble, which represent evil and wrong doctrines, idols of the heart, and philosophies that exalt themselves against God.
4. Fire PURIFIES things of value which we do want to retain. The analogy is used in the Scriptures of purifying gold by fire to make it more beautiful and more valuable. Gold represents the highest doctrines of spiritual understanding such as the Love of God and the Sovereignty of God, and salvation of all.
No one teaches us more regarding the fiery trials of life than the apostle to the nations, Paul. Paul was "revealed, tried, salted, and baptized" in God’s "CONSUMING FIRE," and yet never a single hair on his head was ever singed.
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Calling attention mostly to # 3 above. It may not exactly 'define'
idols of the heart, but placing it with 'evil and wrong doctrines and philosophies' helps explain what 'idols of the heart' are.
I'm not sure every weakness, failing, and "diseases of sin and carnality" are "idols of the heart". A better example would be belief in the myth of free-will. That's an 'evil and wrong' doctrine that is not only held 'intellectually' but also affects our lives.
Either way, they will come under fire.