But the situation can be more subtle than that. The Bible certainly gives us the clear affirmation that to be a true Christian we must have the Spirit of Christ – of God – within us, or we simply are not what we think we are. The apostle Paul makes that clear in his letter to the Romans:
“You, however, are not in the realm of the flesh but are in the realm of the Spirit, if indeed the Spirit of God lives in you. And if anyone does not have the Spirit of Christ, they do not belong to Christ” (Romans 8:9).
If we do have that Spirit acting in our lives, Paul tells us, there will be clear “fruits” or evidences (Galatians 5:22-23). But it’s often easier to see those fruits in the lives of others than it is within ourselves. That’s especially true if we tend to be a naturally outgoing and accepting person, a person with a fair measure of natural human patience or other good quality. Hopefully, as Christians, we can see growth in our lives regardless of where we started on the "goodness curve," but as C.S. Lewis famously argued, some do start out higher on the curve.
Perhaps that is why Paul gave another clue in Romans – an actual “litmus test” if you like – as to what it looks like to be truly acknowledging God in our lives. But he did that in a place and a way that you might not have noticed:
“For although they knew God, they did not honor him as God or give thanks to him … And since they did not see fit to acknowledge God, God gave them up to a debased mind to do what ought not to be done” (Romans 1:21, 28).
Now when we read these verses it is easy to see them as only applying to those without God – the pagans and God-rejecting individuals of whom Paul was apparently speaking in Romans 1. But we should not miss the obvious broader application of what Paul says. He doesn’t say that he is speaking of those who don’t know God, but of those who do (vs. 21). Paul speaks of individuals who do know God but who demonstrate two very telling signs: they don’t honor God and they don’t give thanks to him.
But why would we apply this to apparent believers – especially if it is not the group Paul was primarily speaking of? The perhaps unexpected answer is found in the word “debased.” We read this word with our understanding of the English concepts behind it and think only of moral or spiritual degeneration. But the Greek word Paul wrote holds a very different significance. The word “debased” in Romans 1:28 is translated from a-dokimon, a word used of precious metals and coinage and meaning not standing up to a test of authenticity, not approved – in other words, fake or counterfeit. The word was, in fact, regularly used of counterfeit money.
So Paul’s point is that God allowed people who knew him (and that could be the God-rejecting or the nominally God-accepting) to take on a counterfeit mind – a counterfeit Christianity where that applies – but the reason was not doctrinal lack of understanding; it was because they failed the tests of honoring God and thanking him.
It’s natural to think that theological litmus tests should be more complex or involve more intellectual issues. But Paul makes it clear that the most basic yet profoundly true tests of whether we are reacting properly to our knowledge of God and living as true Christians – or whether we are a counterfeit – are found in if we honor God in what we think, say and do, and if we give thanks to him. These are things that we can usually see and know about ourselves no matter where we started on the curve.
Fortunately we can use this knowledge. Being aware of these principles is one way we can avoid counterfeit Christians – and I don’t mean the kind we might see in church, but the kind we never want to see in the mirror.