"You believe that there is one God. You do well. Even the demons believe--and tremble!"
This is commonly used to suggest that believing (in Christ, presumably) is not really enough for salvation… that we, like the demons, might also tremble if all we do is believe.
This understanding has three basic problems which reveal that this usage is a misapplication and misunderstanding of this verse.
The first problem might already be obvious: "You believe there is one God… even the demons believe…" This might be useful for understanding our salvation if our salvation was contingent on us believing there is one God. But this is not the case… our salvation is contingent only on believing in (trusting in) Jesus Christ. In other words, the person who "merely believes" that there is one God isn't saved. So yeah, I guess they could tremble. Big deal. I don't see how this is helpful at all if that's a proper understanding of the verse.
The second problem is that there is no plan of salvation for demons… certainly not a plan of salvation that involves faith in Christ. Christ died for the sins of humans, He didn't die for the rebellious angels. With this in mind, it's hard to imagine how this verse informs us about our own salvation at all. The demons tremble not because their belief that there is one God isn't "enough" to save them. They tremble because they know good and well that their days are numbered and that there's no way out for them. Their trembling has nothing to do with what they believe or don't believe. And I would say, based on Luke 4:41, that demons know full well who Jesus Christ is, also:
"And demons also came out of many, crying out and saying, "You are the Christ, the Son of God!" And He, rebuking [them], did not allow them to speak, for they knew that He was the Christ."
So the demons believe and tremble. Considering what is required of us for salvation (faith in Jesus Christ) and considering that salvation isn't available at all to demons, it's clear just based on these two ideas that this verse tells us nothing about how we are saved.
The obvious question, then, is what did James mean by this and why is it there?
Well this brings us to the third problem… were these words a reflection of James' own thoughts? It turns out there's good reason to question that. I'll begin a new post here to deal with that, as this does get a bit tricky.