From my early childhood I remember the warning against counterfeit money. I have no idea if I ever actually handled any counterfeit bills but I know that the counterfeiters have done everything they could to try to fool the government. And the government has done everything it could to make it nearly impossible for the counterfeiters to get by their scrutiny.
During the Personal Evangelism class I took at my Bible college years ago our instructor used the idea of counterfeiting as an illustration of the devil's attempt to fool people with false presentations of Christianity and of Jesus Himself. He said a couple of things that always stuck with me.
First, he said you don't find counterfeit paper bags or notebook paper. Why not? Those items have no real value and what would be the sense of bothering with them? If you're going to counterfeit something, at least counterfeit something of value, especially money. And don't just start with dollar bills. Go for the $20 or $50 or even the $100 dollar bill. They're worth something and if you can fool a store keeper with such bogus bills then you might walk out of the store with a wealth of merchandise.
The idea here is that Satan doesn't try to counterfeit worthless religions or obscure prophets. Satan goes for what is of value, namely, Jesus! The devil has worked though so many different people claiming to be Christ. I remember the Sun Yung Moon movement back in the 1970's and 80's. Moon was described as a modern day Messiah. It's hard to believe just how many young people were sucked into his deceit. The same can be said of David Koresh of the Davidians of Waco, Texas. Or take Jim Jones who led over 900 people to commit suicide in Guyana. Satan will always have his counterfeit "Christ's" showing up. Don't be deceived!
The second point my evangelism professor said was that the treasury agents who guard the currency don't spend time examining and studying all the counterfeit bills that are out there. They concentrate on studying the "real deal"; the real money! They get to know the true currency so well that they can spot a phony bill in a flash! And that's what Christians need to do with the truth of God. Get to know the truth of Scripture; get to know the real Christ, not only studying what the Bible has to say about Him, but get to know Him personally yourself. Get to know Him so well that you can spot a phony "in a flash!" How well do you know your Savior? Spend time with Him every day and learn what the Word of God says about Him so you "won't be deceived."