Here’s one such way: ask, “Were any of the groups that broke off from the visible Church in the first millennium correct to do so?” This question can prompt a deeper discussion about the nature of the Church (as visible, and as divinely protected) and about the problem of schism.

If you’ve spent any serious time in dialogue with Protestants, you’ve probably found yourself running into a wall. The arguments that you find so persuasive, the Bible passages that seem so clearly Catholic, don’t strike your Protestant friends or family as particularly compelling. Their personal interpretation isn’t the same as yours (or the Church’s), and they’re not sold on the importance of deferring to the Church’s interpretation rather than their own.

Schism comes from the same root as schizophrenia: the Greek word σχίσμα (schisma). Schizophrenia literally means “a splitting of the mind,” and St. Paul warns the Body of Christ not to become schizophrenic. Instead, we are called to “stand firm in one spirit, with one mind striving side by side for the faith of the gospel,” and to have “the same love, being in full accord and of one mind” (Phil. 1:27, 2:2). Thus, he condemns “dissension” and “party spirit” as “works of the flesh,” warning that “those who do such things shall not inherit the kingdom of God” (Gal. 5:19-21).

In saying all of this, Paul’s merely spelling out what is implicit in Jesus’ prayer in John 17:20-23, in which he prays for future believers (us!) “that they may all be one; even as thou, Father, art in me, and I in thee, that they also may be in us, so that the world may believe that thou hast sent me,” and that these future believers “may become perfectly one, so that the world may know that thou hast sent me and hast loved them even as thou hast loved me.”

If Jesus desires perfect unity within the Church for the sake of the witness of the gospel, then our schisms are a flaunting of his desires and a counter-witness to the gospel. Such an action can only be a work of the flesh, unless Jesus is himself schizophrenic.

But this whole idea of schism presupposes the existence of a divinely originated and visible Church, and we see just such a Church described in the New Testament. In Matthew 16:18, Jesus says to Peter, “You are Peter, and on this rock I will build my church.” You may have argued a thousand times about the meaning of “on this rock,” but this time focus now on the promise, “I will build my church.” It means that the Church’s origins are divine.

And what does this Church look like? Well, later Jesus says that if your brother resists your attempts to correct him, you must ultimately “tell it to the church; and if he refuses to listen even to the church, let him be to you as a Gentile and a tax collector” (Matt. 18:17). If the Church isn’t visible, how can it be the final appellate court for Christian disputes? We see this divinely originated visible Church throughout the book of Acts and indeed all of Church history.

I should note that this isn’t a trick question but a way for your friend to better understand Church history. It may be that he doesn’t know enough about Church history to answer confidently. If that’s the case, encourage a deeper study of the history of the early Church, and especially encourage him to read the Church Fathers in their own words. Not a few Protestants have been drawn to Catholicism in just this way, vindicating the famous line from Cardinal Newman (himself a convert) that “to be deep in history is to cease to be a Protestant.”

But let’s suppose that your friend does know enough about Church history to answer the question. How might he answer? Well, he might say that these break-off groups had some legitimate grievances. True enough: the Donatists, for example, were scandalized that some Catholic bishops had caved to Roman persecution, going so far as to turn holy things over to the imperial troops to be destroyed. Sometimes, heresies and schisms were popular because the clergy of the Catholic Church behaved scandalously.

But this is a point worth pressing: are we called to break off communion with sinners? When the servants of the householder in the parable of the wheat and weeds asked permission to weed the wheat fields (representing the Church), he told them, “No; lest in gathering the weeds you root up the wheat along with them” (Matt. 13:29). Should the earliest Christians have rejected the apostles because Judas was so rotten? So we can grant, then, that most heretics and most schismatics throughout history have had some legitimate grievances, but that didn’t make their heresy or schism okay.

At this point, your friend might double down and try to defend the various heretical and schismatic movements of the first millennium. This gives each of you a chance to learn more about these movements and your friend a chance to decided whether he really wants to be associated with people who (for example) denied the Trinity or the two natures of Christ.

But rather than putting himself outside mainstream Christianity in that way, your friend will more likely eventually conclude—perhaps after much research—that each and every single time a schism or heresy arose in the early Church, the visible Church was right, and the new movement was wrong.

This raises two obvious questions. Was it just a lucky coincidence that the visible Church got it right every single time on subtle, nuanced questions like christological and trinitarian doctrine? And why should we think that this same Church (which is either incredibly lucky or guided by the Holy Spirit) suddenly got it wrong in the sixteenth century?