"You cannot serve both God and Money." - Jesus
Our teacher couldn't say it more simply. But we in America feel the need to test it, I guess, just to be sure.
The god of money (wealth, stuff, material things, etc.) is identified by Jesus by the name of Mammon. The interesting part is, there is no god found in any of the ancient cultures with that name. He has no excavated shrines or temples, nor is he mentioned in any historical society's documents or engravings.
Why is that, you may ask? Best I can tell, it's because mammon was merely the common Arabic word for money, possessions, or material assets. It was as commonly used in Jesus' day among Arabic speakers as the word "money" is now among English speakers. They no more thought that they were calling on the name of god when they said "mammon" as you think you are when you say "money".
It was Jesus, with his statement above, that first touted mammon as Mammon. He was serving a warning: Mammon isn't just mammon, Mammon is an entity that is in opposition to God.
For effect, read that paragraph again replacing "mammon" with "money".
We spiritual-types don't believe it. We use money to serve God, we don't serve money. Money is a neutral thing that can be used for good or evil. "It's not how much stuff you have, but how you use it." And it is all true.
But we should be slow to assume that money hasn't become an idol in our lives. Subversively, invisibly, and unnoticeably money, as Jesus exposed, becomes Money. But how do we test ourselves?
One way to test is worry. If you worry about money, Mammon at least has a grip. Another one is relationships. If you can't have a deep, meaningful relationship without spending money to enable it, Mammon has deceived you. Another test lies in the areas of rest, comfort, and pleasure. If you can't find these for your heart without the use of money, then Mammon has your heart.
I would go this far with it: if the only way you feel like you can give to and serve and advance the Kingdom of God requires money, and that without money, you can't give and serve in God's Kingdom in the way you want to, then money has become Money.
In a Mammon-saturated society like ours, let's err on the side of assuming that this idol is probably present in our lives...and work towards getting it out.