Lutherans and the Reformed agree on many things. They disagree about how far Christ’s death reaches. Lutherans deny that Christ died only for the elect. They hold that Christ died for every person without exception, and that at the cross he gave eternal life to everyone, not just to those who will believe.
1 John 5:11 gets used to make this case. The verse says, “And this is the testimony, that God gave us eternal life, and this life is in his Son.” Read “us” as “everyone, without exception,” and it looks like Scripture is saying God has already given eternal life to every person.
But some people die in their sins. They don’t have eternal life. So a Lutheran reading the verse this way has to split justification into two parts to hold both claims at once. The first is objective justification: Christ died for everyone, and at the cross God gave eternal life to everyone, whether or not they end up believing. The second is subjective justification: a person actually receives and possesses that life only through faith. On this view Christ didn’t just make salvation possible for every person. He actually gave it, at the cross, to every person. Faith is how you come to possess a life you already, in some sense, have.
A Reformed reader takes “us” in verse 11 differently. “Us” means believers, the people John is writing to and about throughout the letter, not every human being. God gave eternal life to his people, in his Son, and a person comes to have that life by coming to have the Son.
A Lutheran named Jeremy argued against the Reformed reading with a reductio.
A reductio, short for reductio ad absurdum, works by assuming your opponent’s position is true, then showing that the assumption leads to an absurdity. And if a position leads to an absurd or self-contradictory result, that’s grounds to reject the position, without having to argue against it head-on.
Here’s Jeremy’s reductio. Assume, for argument’s sake, that the Reformed reading is right and “us” means the elect, not everyone. Under that assumption, the testimony of verse 11 says, in effect, “God gave the elect eternal life, and this life is in his Son.”
Now picture an unbeliever who has heard this and says: “I believe God gave the elect eternal life. I believe that life is found in his Son. I just don’t think I’m one of the elect.” This man has agreed with everything the verse says. He hasn’t denied a word of it. He has only excluded himself from the group the verse describes.
But verse 10 says the one who doesn't believe this testimony has made God out to be a liar. If this man has agreed with everything the testimony states, what has he actually rejected? In other words, how is this man making God out to be a liar if he believes the testimony, word for word, exactly as verse 11 states it? Jeremy's point is that the Reformed reading lets an unbeliever affirm the whole testimony of verse 11 while still counting as someone who has rejected it, and that's exactly what verse 10 says can't happen. Since that's absurd, Jeremy concludes the Reformed reading of "us" has to be wrong, and the testimony has to reach the unbeliever himself.
That argument only works if you grant one assumption: that believing the testimony just means agreeing the sentence in verse 11 is true.
Grant that, and the reductio works. The man agrees with the sentence, so under the assumption he’s believed the testimony. But he’s also still an unbeliever, since he hasn’t come to Christ. So you get a man who has believed the testimony and is still an unbeliever, and verse 10 says that can’t happen. Something has to give, and Jeremy says it’s the Reformed reading of “us.”
An argument can be valid and still be wrong. Validity is a claim about structure: if the premises are true, the conclusion has to follow. It says nothing about whether the premises are actually true. A valid argument can run on a false premise and still be valid, because "valid" only means the reasoning holds together once you grant what it assumes. Soundness is the further claim that the premises are actually true, and only a sound argument gives you a conclusion you're obligated to believe. Jeremy's reductio is valid. If believing the testimony just means agreeing that the sentence in verse 11 is true, then his unbeliever has believed the testimony, and that would contradict verse 10. The logic is valid once you grant the assumption. But the assumption itself is the problem.
Verse 10 doesn’t say believing the testimony means agreeing a sentence about it is true. It says, “Whoever believes in the Son of God has the testimony in himself.” Believing the testimony, in John’s own words, is believing in the Son. That’s trust in a person, not agreement with a report about him. The man in Jeremy’s illustration agrees with a sentence about the Son. He hasn’t trusted the Son. He was never a case of someone who believed the testimony to begin with, and no contradiction has been produced.
Someone might object that a person can believe a report is true without receiving what the report describes. That’s true of reports about things that happened to other people. It isn’t how John frames this testimony. Verse 12 says, “Whoever has the Son has life; whoever does not have the Son of God does not have life.” That isn’t a report about something that happened to somebody else once. It’s a standing condition, open to anyone who comes to have the Son, and John treats coming to Christ and believing in him as the same act elsewhere: “Whoever comes to me shall not hunger, and whoever believes in me shall never thirst” (John 6:35).
The whole argument turns on one question: does agreeing with a sentence about the Son count as believing in the Son? John says no.
The stakes in that question aren’t only exegetical. If agreeing that a sentence about Jesus is true counts as believing in him, the same equivocation breaks other things John says in this very letter, and breaks them badly. A few verses before the passage in question, John writes, “Everyone who believes that Jesus is the Christ has been born of God” (1 John 5:1). A few verses after, he writes, “Who is it that overcomes the world except the one who believes that Jesus is the Son of God?” (1 John 5:5). Both are the same construction as verse 10, believing something to be true of Jesus. If believing, in that construction, just means holding the corresponding sentence to be true, the demons qualify! According to Luke, “demons also came out of many, crying, ‘You are the Son of God!’ But he rebuked them and would not allow them to speak, because they knew that he was the Christ” (Luke 4:41). The demons affirmed both sentences John names here, Son of God and Christ, and they affirmed them as beings with direct, unmediated knowledge that the sentences were true. Nobody wants to conclude from this that demons have been born of God and have overcome the world. But that is exactly where the propositional reading leads once it is let loose on the rest of the letter. John is not just handing out a checklist of true sentences for a person to assent to. He is describing what it is to actually hold to Christ, to trust him, to cling to him as Lord and Savior. That is precisely what the demons, for all their correct information about him, refused to do.
Once you see that agreement with a true sentence isn’t the same thing as belief in the Son, Jeremy’s man was never a counterexample to anything. He agreed with a sentence and refused the Son. That is exactly the unbelief verse 10 is talking about.