God will protect the entire church, all Christians, along with the visible church (congregations, including Catholic & all others).
It’s like a divine checks and balances system (did I just coin a new theological theory)
Unity will happen at the end when the earthly churches are replaced by the New Jerusalem, the coming kingdom (see Rev. 21, Gal. 4) – until then man cannot be trusted with absolute power, because it corrupts absolutely.
Christ didn’t stop working at His death. He is still guiding the faithful. He didn’t hand the reins over to the Romans and stop working for us. When God saw the abuses in the Roman church He reached down and used Luther to correct it (I admit – God sometimes chooses peculiar people to do His work). Whatever can be said about Luther imagine if he never existed?
The reformation gave this world so much. Imagine – we might still have guys like Johann Tetzel running around charging us money to free grandma from purgatory. Luther even compelled Rome to reform, making the RCC a better church. What would have become of science, would the English ever have colonized the new world, would we have ever had an enlightenment and men like John Locke and Adam Smith …
I doubt it. The fruits of the reformation and enlightenment are still paying dividends for this world. Because of America communism fell, the Nazi’s defeated, and economic prosperity is spreading throughout the world. Soon religious freedom will reach all corners of this globe and inevitably Jesus’ name will be praised in all nations. God is great!