One argument for Catholicism whose popularity has waned in the past few centuries is the argument from miracles. Whereas you may think miracles are a way of showing atheists that God exists (and they are), throughout history, these arguments were actually used more often with religious people who needed evidence that the Catholic Church has a divine foundation.
In the Summa Contra Gentiles, St. Thomas Aquinas explains why God did not repeat the miracles performed in the Old Testament or apostolic age throughout Church history and that the mass conversion of believers was itself a sign of the Church’s truth. But he adds, “Yet it is also a fact that, even in our own time, God does not cease to work miracles through his saints for the confirmation of the Faith” (1.6.1). The Protestant Reformers even discussed the argument from miracles and how they would answer it against their own movement, which lacked miracles to verify its God-given origin.
In a preface to the Institutes of Christian Religion, John Calvin admits that Protestants don’t have miracles to validate their claims as Catholics do. But he explains this discrepancy by claiming that the Reformers are only reaffirming what the apostles miraculously taught, and so miracles aren’t needed, since the Reformers’ preaching does not need miraculous authentication. However, Calvin also claims that miracles would be found only in apostolic churches, which means that Catholic miracles have to be false. He writes,
They allege miracles which might produce wavering in minds otherwise well disposed; they are so frivolous and ridiculous, so vain and false. . . . It becomes us to remember that Satan has his miracles, which, although they are tricks rather than true wonders, are still such as to delude the ignorant and unwary.
So, according to Calvin, Catholic miracles could be deceptions or demonic, but they can’t be divine acts, because Catholicism is not apostolic in nature. Some Protestants go even farther and say the Bible teaches that all miraculous gifts ceased with the death of the apostles. (These Protestants are appropriately called cessationists.) Protestant pastor John MacArthur once said in an interview that Catholicism is false because it is tied into a false continuationist model that claims that God is still giving revelation and miracles. MacArthur prefers a model that says the deposit of faith was handed down once in the past and then preserved only in Sacred Scripture (i.e., sola scriptura). He said,
You have, I think, that wonderful statement in Jude this is the Faith once for all delivered to the saints. You have a faith packaged by divine revelation once for all delivered. It doesn’t keep going and keep going. . . . One of the errors in Roman Catholicism is that they don’t have any end to the true canon of divine revelation; it just keeps going and going and going, and that’s their affinity with the charismatic movement, where you continue to have people having revelations and revelations.
First, the Catholic Church affirms that public revelation ceased with the death of the last apostle or apostolic man, like Mark or Luke. However, God can still reveal himself to people or groups, though he does not bind all the faithful to accept this private revelation (see the Catechism [CCC], paragraphs 66-67). And part of this private revelation can include miracles or giving the faithful miraculous gifts or charisms.
Also, using Jude 3 to prove that public revelation has ceased doesn’t work because it confuses “giving the Faith” to the saints with public revelation. Jesus gave “the Faith” once and for all to the apostles, but the public revelation of the Faith continued for decades after his interactions with them during the writing of the New Testament. There isn’t any explicit biblical evidence that this revelation ceased after the death of the last apostle (or that it didn’t continue for centuries rather than decades). There is also no evidence that there were no more living apostles who could give such revelations. Our knowledge about these things instead comes from Sacred Tradition, and so we agree that the deposit was given “once for all,” but we deny that it is confined to Scripture.
Many Protestants do believe that the Bible’s teachings about spiritual gifts do not have an expiration date. Unlike those who think spiritual gifts have ceased, or cessationists, they believe that those gifts continue in the Church, which is why they call themselves continuationists. I like this warning from cessationist Tom Pennington. He says that Protestants who believe in the continuing gifts of the Holy Spirit leave themselves open to accepting the continuing authority of the apostles and Church leaders who regulated the use of those gifts. He writes, “When charismatics state their case against cessationism as [Protestant author Andrew] Wilson does, they unintentionally also surrender the field to apostolic succession.”
So if you are dialoguing with a Protestant who happens to hold a continuationist view, then you actually have good common ground to show the reasonableness of our faith. In this case, if he says it makes sense to believe that the gifts of the Holy Spirit given to the apostles continued past the apostolic age, then it makes sense to say the authority given to the apostles continued past the apostolic age as well. And one sign of that authority would be the innumerable miracles associated with the Catholic faith, including Eucharistic miracles, the miracle of Fatima, incorruptible saints, and many more—all of them just waiting to be shared with believers who are open to identifying God using miraculous revelation to confirm the ordinary means he has given us divine revelation: through the one, universal Church he founded.