The Roman Catholic challenge—“So which of the many different doctrines of non-Catholic churches is the truth? All claim to be true but differ from others! Can’t all be true if they differ!”—is a logically flawed, theologically inconsistent, and self-defeating argument. It assumes that the mere existence of doctrinal disagreement within Protestantism invalidates Protestantism itself. However, by this same standard, Roman Catholicism would also be invalidated since it has its own significant doctrinal divisions. Furthermore, the argument fails to address the real question: What is the ultimate standard of truth? Truth is not determined by institutional unity but by divine revelation—God’s Word alone.

If doctrinal division within Protestantism disproves Protestantism, then doctrinal division within Catholicism must also disprove Catholicism. Throughout history, Catholic theologians have been deeply divided on crucial doctrines, from the nature of grace (Thomists vs. Molinists), to the extent of papal authority (Conciliarism vs. Papal Absolutism), to moral issues (traditionalists vs. modernists). Even today, Vatican II Catholics and traditionalist Catholics reject each other’s interpretations of doctrine—so by their own logic, Catholicism would be false. Worse still, Catholicism is just another church making a truth claim, meaning doctrinal disagreements within Protestantism would also invalidate Catholicism, since it is one among many competing voices. The argument collapses under its own weight.

The real question is not which denomination has perfect external unity, but which doctrine aligns with God’s authoritative revelation. Catholics assume truth is determined by institutional authority, but Scripture never teaches this. Jesus and the apostles did not establish an infallible ecclesiastical hierarchy as the source of truth—they pointed people to the Scriptures. “Sanctify them in the truth; Your word is truth.” (John 17:17) Truth is found in God’s Word alone (Sola Scriptura), not in a human institution claiming infallibility. Doctrinal disagreement does not negate truth; it only proves that sinful men struggle to rightly divide the Word of God.

Thus, the Catholic argument from doctrinal division is a smokescreen to avoid addressing the real issue: What does Scripture teach? The gospel is not found in submission to a religious institution but in faith alone in Christ alone, as revealed in God’s inerrant Word. Doctrinal disagreement among fallible men does not change the fact that there is one absolute truth, revealed in Scripture. The Roman Catholic Church is not the arbiter of truth—God’s Word is. Instead of appealing to institutional unity, Catholics must confront the question they are desperately avoiding: Does their doctrine align with Scripture? Because when tested by the Word of God, it is Rome, not Protestantism, that stands condemned.