If you are judging the Catholic Church’s teachings by the Bible, as Luther did, then they were corrupt for a whole lot longer than the 240 years you suggest. Very early on, the Catholic Church in Rome took it on themselves to make serious alterations to the Ten Commandment Law of God, even as had been predicted would occur in passages such as Daniel chapter 7, where a “Little Horn Power” rising from the area of Rome would “seek to change times and laws”.

The Papal Church, in order to incorperate as many of those of other religions into their ranks as quickly as possible, shifted the day of public worship from the seventh-day Saturday Sabbath prescribed by the fourth of the Ten Commandments, to Sunday, the first day of the week. This was the mark of Roman Papal authority, and spread from that city over the course of many centuries to now embrace nearly the entire Christian world in worship that is in violation to God’s Ten Commandment Law as expressed in the Bible.

The Papal Church was also interested in not disturbing the worship practices of the many groups who worshipped idols. So they eleminated the second of the Ten Commandments, the law that forbids making images and bowing down before them and worshipping them. Now they only had nine commandments, instead of ten. So they split what had been the tenth commandment, against coveting, into two parts. Instead of not coveting your neighbors wife or property, as before, there were two commands against coveting. You couldn’t covet his wife. You couldn’t covet his property.

These attempted alterations were successful in swelling the ranks of the papal church with many who continued to worship on the “venerable day of the sun” which was the day popular in Rome among the worshippers of Mithra in those early centuries, and also in incorperating many idol worshippers into Christian ranks. Often, the same idols that had been worshipped before were simply renamed after Christian saints and continued to be worshipped in the same temples.

In this way, may of the practices and the beliefs that were part of paganism, and had no part in Biblical Christianity at all, were brought into the Catholic Church. This did not become well-known until the Enlightenment, when people began studying ancient literature of all kinds. When Luther began studying the Bible, which was not available to the common people in their own language at the time, he found a great deal of the teachings and practices of the Roman Church of which he was a priest to be in violation to its teachings and its recomendations. He said, “We need to obey the Bible, rather than the pope!” That’s what resulted in the Catholic-Protestant split.

As for Luther’s reform resulting in the death of 100,000 persons due to his opposition to the Papacy, that’s rather undershooting the entire body count that has resulted from Papal persecutions. Again, Daniel chapter 7 declared centuries before the Papacy’s rise, that it would be a persecuting power that would “seek to wear out the saints of the Most High”, that is, fight against those who were actually being loyal to God and to His commandments rather than going along with the mixture of true and false that came from mixing paganism with Christianity in the Papacy. In fact, somewhere between 50 and 200 million were killed due to Papal involvement and influence and to extend its powers.

One should know that all of the major Protestant reformers, including Martin Luther, John Knox, Zwingle, and the rest were in agreement that not only should the Bible be held as the corrector of teaching and practice for the individual Christian as for the church as a whole, but also that the Papacy was in fact, the prophetic fulfillment of the “little horn” power of Daniel 7, and the “Man of Sin” in Paul’s letter to the Thessalonians. This was the intellectual framework for their willingness to withdraw from Rome’s fellowship in protest, the very bedrock of Protestantism.

It was so convincing and successful that the pope of the day called a council to attempt to get the finger of prophecy that pointed to his own activities off of him and directed somewhere else. Two Jesuit scholars, Alcazar and Ribera, came back with alternate explanations of the “little horn power” and the “man of sin” in the Biblical prophecies. One said the “little horn” was a Syrian ruler from before the time of Jesus who had desecrated the temple. Therefore, all prophecies of this sort were far in the past and should not be examined in relation to the Papacy’s activities. The other said, “No. Antichrist is a renegage Jew who will arise far in the future just before Jesus returns and cause great devestation.” Again, no need to examine the prophecies as they had been fulfilled in the centuries long activity of the Papacy, since their fulfillment wasn’t right there in front of everybody, but either far in the past, or far in the future.

The pope saw these conflicting and mutually exclusive views and said, “Yes! Teach them both.” So that’s what the Counter Reformation did. And, plainly, it was a successful strategy. Now nearly all of the Protestant Churches embrace one or the other of these views, and have long ago abandoned the method of interpreting prophecy that Martin Luther and their founders once championed.

For those who wish to study this matter further, Martin Luther is not only the Father of the Protestant Reformation, but also the Father of the Historical Interpretation of Bible Prophecy–which basically holds that the prophecies were given and began to unfold in history, stretching from the day they were given to such prophets as Daniel until the return of Jesus. This method of interpretation clearly identifies the Papal power as the “little horn” power opposed to God and His people, and also as the “Man of Sin” warned against by the apostle Paul. The other two options, which came from the Jesuit scholars in their original form, are Pretertism, which holds Antiochus Epiphanese is the antichrist little horn power, though his activities do not match the specifications of the prophecies in full, and Futurism, which says antichrist is a charismatic figure that will arise in the future and cause great ruin prior to Jesus’ return.

These are important issues, and ones that many even who hold the name “Protestant” have long ago forgotten as they have embraced views that came from the Counter Reformation councils of the Papacy that followed Martin Luther’s Reformation.

I would suggest the book “The Great Controversy” by Ellen White, as a good overview of these matters from a viewpoint that is closer to Luther’s days and views than those now held by the Church called by Luther’s name. These things are not secrets. They are a part of Christian history. It is just that they have been forgotten by those who should remember.