Although I cannot locate a specific quotation, at one point I had heard that Pope Benedict encouraged his fellow Roman Catholics to read the early Luther, when Luther was still genuinely catholic. The problem with this, of course, is that the core theological convictions of the “early Luther” were part and parcel of his later protest. One cannot readily separate Luther the responsible RC theologian from Luther the Church reformer, for the theology drove the reform. Now of course, I do not want to discourage such developments, but speaking honestly, it is very difficult for me to understand how Roman Catholic theologians who are familiar with Luther think that his early pre-Reformation works will end up helping their cause! It seems to me that the crises of indulgences became particularly clear for Luther precisely because of the theologian he had become, and he was absolutely determined to “refute the opinions of the ‘new’ scholastic doctors concerning the efficacy of indulgences” (Hendrix, p. 35) And from this starting point, it was only a matter of time before Luther was able to identify and articulate ever more clearly how the related issues of sacramental penance and absolution (see 10, 11 and 12 below) had been wrongly taught by the Roman hierarchy (as he found that the problem went deep, i.e. Aristotle vs. Bible – see 13 and 14 below [also see this post dispelling myths about the Lutheran view of "Sola Scriptura"]). One link in the chain led to another which led to another – until Luther was able to see clearly the very heart of the matter: that is, the essence of the Gospel itself. The controversy regarding indulgences had brought him there.I vaguely recalled a report that the pope said something like this, so after snooping around a bit I found this 2005 ZENIT article: LUTHERAN HAILED CARDINAL RATZINGER AS EXPERT ON LUTHER.
"During the debate on the encyclical "Fides et Ratio," which took place in Rome in October 1998, Cardinal Ratzinger revealed that before entering university he had already read all of Luther's works written before the Reformation."
"Ratzinger invited those present to read those writings again, as they express the great battle that Luther had with himself to live and accept the teachings of the just and good God," she added. "'Dear Protestant friends, rediscover the Luther of those years,'" recommended Cardinal Ratzinger at the time."Now, if you read the article, it appears what's being reported is not an actual writing or transcription from the Pope. Rather, it's the recollections of someone hearing the Pope speaking in a public meeting. I'm not sure if this is the source Nathan had in mind.
I would though agree with Nathan that the early Luther is not as Roman Catholic as modern-day Roman Catholics. In fact, it wasn't uncommon to find Roman Catholic writers of previous generations arguing Luther's Romanism was defective even before 1517.