Ex 20:4"You shall not make for yourself an idol."

Idolatry is the worship of some image or representation of spiritual power. Worship of the creature instead of the Creator is a form of idolatry. Paul described it this way, Rom 1:21-25-- "For even though they knew God, they did not honor Him as God or give thanks, but they became futile in their speculations, and their foolish heart was darkened. Professing to be wise, they became fools, and exchanged the glory of the incorruptible God for an image in the form of corruptible man and of birds and four-footed animals and crawling creatures.
Therefore God gave them over in the lusts of their hearts to impurity, so that their bodies would be dishonored among them. For they exchanged the truth of God for a lie, and worshiped and served the creature rather than the Creator, who is blessed forever. Amen.

The curse placed upon idolaters is recorded in Deut 27:15--"Cursed is the man who makes an idol or a molten image, an abomination to the LORD, the work of the hands of the craftsman, and sets it up in secret.' And all the people shall answer and say, "Amen.'

Anything we place between us and God may become an idol, receiving our devotion in the place of God. Some have even suggested that Church buildings can become an idol if our focus is on the building, and activities within the building, rather than on pleasing God in our lives every hour.
Those with mature faith may realize that an idol is nothing, and not be tempted to think that there is any power in stone, wood, brass, or gold. But idolatry is a problem for those who are trapped in ignorance. Idolatry robs God of the honor and devotion that is due Him, and causes worshippers to substitute ritual and tradition in place of a life devoted to service to God and mankind.

Isaiah described the foolishness of idolatry, Isa 44:8-20--Those who fashion a graven image are all of them futile, and their precious things are of no profit; even their own witnesses fail to see or know, so that they will be put to shame.
Who has fashioned a god or cast an idol to no profit? Behold, all his companions will be put to shame, for the craftsmen themselves are mere men. Let them all assemble themselves, let them stand up, let them tremble, let them together be put to shame.
The man shapes iron into a cutting tool and does his work over the coals, fashioning it with hammers and working it with his strong arm. He also gets hungry and his strength fails; he drinks no water and becomes weary. Another shapes wood, he extends a measuring line; he outlines it with red chalk. He works it with planes and outlines it with a compass, and makes it like the form of a man, like the beauty of man, so that it may sit in a house.
Surely he cuts cedars for himself, and takes a cypress or an oak and raises it for himself among the trees of the forest. He plants a fir, and the rain makes it grow. Then it becomes something for a man to burn, so he takes one of them and warms himself; he also makes a fire to bake bread. He also makes a god and worships it; he makes it a graven image and falls down before it. Half of it he burns in the fire; over this half he eats meat as he roasts a roast and is satisfied. He also warms himself and says, "Aha! I am warm, I have seen the fire."
But the rest of it he makes into a god, his graven image. He falls down before it and worships; he also prays to it and says, "Deliver me, for you are my god."

We easily see the folly of worshipping an image made by a craftsman. But we may worship things that are just as foolish. Unrighteous desire for the things of this world is idolatry. We worship what we trust. Greed is idolatry, Col 3:5-6--Therefore consider the members of your earthly body as dead to immorality, impurity, passion, evil desire, and greed, which amounts to idolatry. For it is because of these things that the wrath of God will come upon the sons of disobedience,--.

Trusting what we have done with our own hands rather than trusting the God who created us and made all good things possible is idolatry.