In a 1944 essay, “Christian Reunion: An Anglican Speaks to Roman Catholics,” published in Essay Collection and Other Short Pieces (edited by Lesley Walmsley, London: HarperCollins, 2000, 395-397), C. S. Lewis wrote:

The difficulty that remains, and which becomes sharper as it becomes narrower, is our disagreement about the seat and nature of doctrinal Authority. The real reason, I take it, why you cannot be in communion with us is not your disagreement with this or that particular Protestant doctrine, so much as in the absence of any real 'Doctrine', in your sense of the word, at all. It is, you feel, like asking a man to say he agrees not with a speaker but with a debating society. And the real reason I cannot be in communion with you is not my disagreement with this or that Roman doctrine, but to accept your church means, not to accept a given body of doctrine, but to accept in advance any doctrine your Church hereafter produces. It is like being asked to agree not only to what a man has said, but what he's going to say.

. . . To us the terrible thing about Rome is the recklessness (as we hold) with which she had added to the depositum fidei -- the tropical fertility, the proliferation, of credenda. You see in Protestantism the Faith dying out in a desert: we see in Rome the faith smothered in a jungle....

I guess Lewis had a very different relationship to the Church than St. Paul did. After all, Paul joined up, and then, lo and behold, the Church had to resolve the big controversy over the necessity of circumcision. And so they had a council of “apostles and elders” to decide on the question: the council of Jerusalem (Acts 15). Paul the great apostle couldn't resolve the dispute on his own:

Acts 15:1-2 (RSV) But some men came down from Judea and were teaching the brethren, “Unless you are circumcised according to the custom of Moses, you cannot be saved.” [2] And when Paul and Barnabas had no small dissension and debate with them, Paul and Barnabas and some of the others were appointed to go up to Jerusalem to the apostles and the elders about this question.

He had to go to the council, which was jointly undertaken by elders (essentially “bishops” in context) and apostles. This is, of course, Church authority (and not Scripture as the only infallible authority, as sola Scriptura teaches), and Paul didn't know beforehand what they would decide.

The Bible doesn't report Paul as proclaiming the truth to the council, in his sublime apostolic authority. He and Barnabas are reported as merely having “related what signs and wonders God had done through them among the Gentiles” (15:12).

At length the council, with the proclaimed direct guidance of the Holy Spirit (15:28), decreed that circumcision was not necessary for Gentile converts. That itself was a conclusion not based on any Scripture that I am aware of. In the old covenant, foreign males who wished to dwell among the Jews and adopt their religious views, had to be circumcised (see, e.g., Genesis 34).

But now the fledgling Church said it was not necessary for Gentile converts to Christianity. This was brand new binding teaching, and seemingly proclaimed without any existing scriptural rationale (the Bible at that time being the Old Testament only).

Therefore, Paul had joined this new Church without knowing what it would decree as non-optional teaching in the future, and how “scripturally based” any new binding decrees would be. He certainly accepted the authority of the Jerusalem council, for Scripture informs us:

Acts 16:4 As they [Paul and Silas] went on their way through the cities, they delivered to them for observance the decisions which had been reached by the apostles and elders who were at Jerusalem.

C. S. Lewis refused “to accept in advance any doctrine your Church hereafter produces.” By this reasoning, Paul should have refused the binding decrees of the Jerusalem council. But he did not. Therefore, Lewis is directly at odds with St. Paul in that regard. He could never have become a Christian in Paul's time, not knowing what would later be in store for him. Or he would have had to leave the Church, following his [false] principle, when the Jerusalem council made its decision.

And indeed, Catholics accept infallible teaching of ecumenical councils, which clarified things like the Trinity and the exact nature of the incarnation of Jesus. Those crucial clarifications were still far in the future at the time of the New Testament: about 225-600 years, in fact.

C. S. Lewis' ultimate, bottom-line theological objection to becoming a Catholic, I submit, is found in his opining on “the recklessness (as we hold) with which she has added to the depositum fidei . . . the faith smothered in a jungle.” That is a critical judgment, and has to be argued, not merely asserted.

I think that if Lewis attempted to argue it (I highly doubt that he ever did at any length, in a published work, because he was very uncomfortable with such discussions), he would be easily defeated by the documented history of the development of doctrine, because he himself accepted the principle of development.

That Catholic developments were genuine and consistent with the existing deposit of faith, was brilliantly demonstrated at length by Blessed John Henry Cardinal Newman, in his Essay on the Development of Christian Dogma. In so doing, he argued himself into the Catholic Church (incidentally, this was the work that put me over the edge, too, back in 1990).

There is simply no way to avoid the authoritative Church in Holy Scripture (see, e.g., 1 Tim 3:15). If a Church (ordained by God) has true authority, it has the power to decree things, and to do so into the future. By joining such a Church, we recognize our own inherent limitations.