IF YOU TOOK chemistry in high school, you may remember playing around with litmus paper, little strips of paper treated with litmus dye. It was part of an educational guessing game. The teacher would give you a beaker of some mystery liquid and ask you to figure out which one it is on a list of choices. You start by dipping a strip of litmus paper in it. If the strip turns red, you know the liquid is an acid (like vinegar). If it turns blue, it’s alkaline (like ammonia). Then you compare the strip to a color chart to see how acidic or alkaline it is (its pH value). That’s the final clue to solving the puzzle.

But even if litmus paper was nothing more to you than a funky little bookmark, you’ve probably heard more generally of a litmus test. Just as litmus paper can be used to decide if a solution is an acid or a base, a litmus test can help one make determinations about people. In the realm of politics, for example, you may be uncertain whether to vote for candidate A or candidate B. One way to decide is to pick an issue that’s important to you and use it as a litmus test; where each candidate stands on that issue determines which way you vote.

Mind you, I’m not recommending single-issue politics as a voting strategy. Getting what you want on one issue may get you what you don’t want on a host of other issues, and in ways you might not notice unless you’re paying close attention. But I get it: the world can be a complicated and confusing place. Sometimes we need a way to simplify things a bit. And in fact, the apostle John provides something like that for his anxious readers, a litmus test for true versus false teaching.

AT THE BEGINNING of chapter 4, as we’ve seen, John warns his readers about the reality of false prophets. Here, we don’t have to envision Elijah dramatically battling it out with the prophets of Baal atop Mount Carmel, complete with the spectacle of fire falling from heaven. John is probably referring to something much more pedestrian, something we can still see today.

Within any Christian community, there can be people who believe they have an authoritative word from God but are actually deceiving themselves. Time and time again, I’ve heard people say, “God told me…” or “I’ve prayed about it, and…” as a preface to saying or doing something questionable. Don’t misunderstand me: I’m not saying that God never reveals himself to people in that way. But I am saying that we are quite capable of being blind to the ways we get it wrong.

“Test the spirits,” John therefore advises in verse 1, “to see whether they are from God.” And in case his readers wondered just how exactly they were supposed to do that, he tells them:

This is how you can recognize the Spirit of God: Every spirit that acknowledges that Jesus Christ has come in the flesh is from God, but every spirit that does not acknowledge Jesus is not from God. This is the spirit of the antichrist, which you have heard is coming and even now is already in the world. (1 John 4:2-3, NIV)

To my ear, the word “acknowledge” here is a little too casual, as when someone nonchalantly says, “Yeah, you may be right.” The underlying Greek word literally means “to say the same thing,” which connotes something more like full agreement. This, then, is John’s litmus test. Any spirit that is in full and enthusiastic agreement that Jesus came in the flesh is from God; any spirit that doesn’t agree with that, isn’t.

What does John mean, though, by “spirit”? As I’ve mentioned before, it’s common to read this passage as being about the kind of spiritual warfare in which people are actually possessed by evil spirits. But think about the story in Luke 4. The chapter begins with Jesus’ temptation in the wilderness, then tells of how he made the people in his hometown synagogue so angry that they tried to throw him off a cliff.

What follows next is a description of his first public miracle: an exorcism (on the Sabbath, of course!) performed in the synagogue at Capernaum. Note what the evil spirit said to Jesus before being cast out:

Go away! What do you want with us, Jesus of Nazareth? Have you come to destroy us? I know who you are—the Holy One of God! (Luke 4:34)

The demon, we might say, had more insight into Jesus’ true identity than anyone else in the room that morning. But it would be a misuse of John’s litmus test to say that the spirit was therefore from God!

John, therefore, is not necessarily talking about false prophets being possessed by evil spirits. He’s talking about people who have so internalized the values and motivations of the world and their culture that it distorts their understanding of the gospel, and they’re trying to convince others to believe the same way. They may even consider themselves to be the truly “enlightened” Christians or to have the Spirit of God, while in reality they’re undermining the cause of Christ. This is why John can once again call them “anti-christ” — they are literally “against Christ” and taking a stance that contradicts the true gospel.

What is that gospel? To use John’s language, it’s that “Jesus Christ has come in the flesh.” That doesn’t mean that this is the only way to summarize the gospel. To some extent, John uses these words because of the specific situation that prompted his letter; he’s giving his people a litmus test for distinguishing the truth about Jesus from the lies told by the false teachers who were once part of the community.

But it’s not all situational. To say that Jesus Christ came to this world as a real live flesh-and-blood human being is indeed a central confession of the Christian faith. We’ll explore why in the next post.