“Swimming the Tiber” is a euphemism for Roman Catholic conversion, as it is the river identified with the Vatican.

Q. What is your only comfort in life and in death?

A. That I am not my own, but belong—body and soul, in life and in death— to my faithful Savior, Jesus Christ. He has fully paid for all my sins with his precious blood, and has set me free from the tyranny of the devil. He also watches over me in such a way that not a hair can fall from my head without the will of my Father in heaven; in fact, all things must work together for my salvation. Because I belong to him, Christ, by his Holy Spirit, assures me of eternal life and makes me wholeheartedly willing and ready from now on to live for him.

Heidelberg Catechism Question and Answer 1

Commenting on the pastoral nature of the creeds and catechisms, Carl Trueman highlights a couple of the questions and answers in the Heidelberg Catechism, especially the way Q&A 1 highlights the heart of the Reformation:

Question 1 shows the glorious Reformation Protestant insight into the fact that assurance is to be the normal experience of every Christian believer and not merely the preserve of a few special saints who have been given extra-ordinary insight into their status before God, as was the medieval Catholic position.

This is perhaps one of the great Protestant insights of the Reformation. We live in an age where conversion to Roman Catholicism is not an uncommon thing among those who have been brought up as evangelicals. There are many reasons for this: some speak of being attracted by the beauty of the liturgy in comparison with what is often seen as a casual and irreverent flippancy in evangelical services; others like the idea of historical continuity, of knowing where the church has been throughout history; still others find the authority structure to be attractive in an age of flux and uncertainty. Whatever the reasons, most Protestants would concede that Rome has certain attractions. Nevertheless, the one thing that every Protestant who converts to Rome loses is the assurance of faith. –The Creedal Imperative, pg. 124

Lest people think Trueman is exaggerating, it must be remembered that Cardinal Bellarmine is reported to have written that assurance is the greatest of all Protestant heresies. Indeed, discussing the subject of assurance with one of my brilliant Catholic professors was one of the most challenging conversations I had in my undergaduate degree. She asked me repeatedly–not threateningly, but forcefully, the way a good philosopher should–how could I be so sure that I was going to be saved? It seemed so arrogant and, well, assured. I’m not sure I gave her the best answer I could have at the time–I mean, I was 20. Ironically though, I realized I was more assured of her salvation than she was.

Trueman continues:

The insight of the Reformation on assurance was key, theologically and pastorally. And, given that it is one thing that every convert to Roman Catholicism must lose, it’s worth noting its priority in the Heidelberg Catechism. The answer is beautifully phrased; and yet if one ceases to be a Protestant, one must cease to claim HC 1 as one’s own. That is a very high price to pay. Speaking for myself, all of the liturgical beauty of Rome, all of the tradition, all of the clarity of the authority structure (and the clarity is often, I think, more in the eye of the beholder than the Church itself) cannot compensate for the loss of the knowledge that I know I have been purchased by the precious blood of Christ that conversion to Rome requires. –Ibid, pg. 125

To be clear, I am not saying that my Roman Catholic brothers and sisters are not saved, or are not actually united to Christ, or can’t experience the Spirit’s wonderful assurance; I know far too many beautifully Catholic people, including my professor, to make that mistake. I am pointing out that formally-speaking, I couldn’t claim it in the sense that the catechism teaches it.

That’s far too precious a thing for me to risk in those waters.

Soli Deo Gloria