Someone told me that Luther had a teaching about the true invisible Church that was a far cry from what could be seen as the Church at his time. Is it true that Luther didn't consider anyone of the Catholic clergy to be a member of the true Church of God?
As an Augustinian monk himself who tried desparately not to leave the church, but rather only to reform it, I think this would be a hard claim for someone to make of Luther.
That said, the "invisible church" or what we moderns would probably call "real Christians" is always a subjective term. I'm sure he thought many clergy weren't truly Christian, but I also know that he thought there were Catholics who were as well. At the very least, Augustine would have been a Catholic clergyman that Luther would have seen as part of the invisible Church, albeit 1000 years predating himself.