Good question

Carl Trueman:

Every year I tell my Reformation history class that Roman Catholicism is, at least in the West, the default position. Rome has a better claim to historical continuity and institutional unity than any Protestant denomination, let alone the strange hybrid that is evangelicalism; in the light of these facts, therefore, we need good, solid reasons for not being Catholic; not being a Catholic should, in others words, be a positive act of will and commitment, something we need to get out of bed determined to do each and every day. It would seem, however, that if Noll and Nystrom are correct, many who call themselves evangelical really lack any good reason for such an act of will; and the obvious conclusion, therefore, should be that they do the decent thing and rejoin the Roman Catholic Church. I cannot go down that path myself, primarily because of my view of justification by faith and because of my ecclesiology; but those who reject the former and lack the latter have no real basis upon which to perpetuate what is, in effect, an act of schism on their part.

Pivoting off of that quote Bryan Cross writes:

Carl carries with him a memory that many if not most Protestants have forgotten, the old ancestral memory of having once been Catholic, before the events of the sixteenth century. He carries within himself this memory of Protestants’ true home and family, understanding that Protestants as such are in essence Catholics-in-exile whose Catholic ancestors in the sixteenth century made the painful decision to live in exile from the Catholic Church until she had sufficiently reformed, never intending to be or form a permanently separate body or group of bodies. This is what Protestant fathers used to teach to their children. But memories are feeble and naturally fade and grow dull with the passing of the centuries. Eventually Protestant fathers no longer taught this to their children, and these children grew up not even knowing that they were in exile. They came to think that schism from the Church was normal, because they no longer retained even the concept of schism from the Church.

They came to believe that the Church Christ founded was not a visible institution, was not even visible at all, even though some still used the term ‘visible Church.’ For many, if not most, the Church is an entirely spiritual entity to which one is fully united by a merely spiritual act of faith, such as a sinner’s prayer. These descendants of the earlier Protestants have completely forgotten that they were separated from anything. And without this memory, there no longer stirs within them any longing for the conclusion of the Catholic Church’s reformation so that they can be reunited to her. Instead, understandably, their discovery of the Catholic Church’s claim to be the one, holy, catholic and apostolic Church Christ founded arouses in them some degree of resentment and offense.

For them, the question “How would Protestants know when to return?” makes no sense, because they have forgotten that they were waiting to return to anything. They have forgotten from whence they came, as Protestants. Carl would have them remember. He would have every Protestant get out of bed each morning asking himself whether there remain any good reasons for not returning to full communion with the Catholic Church. Carl understands that those who have no such good reasons, but who remain Protestant, are perpetuating an “act of schism.” By his prescription, every Protestant should place the following question in a prominent place by his bed, and read it aloud every morning first thing when he gets out of bed, and teach his children to do the same:

Why have I not yet returned to full communion with the Catholic Church?

That's a good question. The provocative point being made by both of these writers is that if you think the Reformation is over, that Luther and Calvin and the rest were all wet, that the doctrine of justification and the nature of the visible church isn't worth fighting over, that we're saved by grace but sanctified by works -- then you have no compelling reason to remain a Protestant. When conscientious Protestant evangelicals such as Richard Neuhaus and Francis Beckwith realized this they followed the path back to Rome. Also, Cross is right to remind those of us who embrace confessional Reformed Christianity that we should do so as those who hope for the day when this breach of our visible unity is healed.