Pastor Larry said:
All Christians have always believed this. But Rome has never taught this.
Pastor Larry, as I understand most Protestant theology, it says that perservering is an evidence of our salvation, not the cause of our salvation. Polycarp and others actually believed, and warned others, that if they did A, they would be damned. It was a warning, not saying, "If you do A you were never saved to begin with" but, "If you do A, you will be damned".
So there is most definitely a difference in how a lot of Christians have viewed salvation. They hailed it as by grace alone, but they also saw the danger of apostasy, both from turning from the teachings of Christ to trust in a false Gospel, and also apostasy in the form of leaving the path of righteousness to trudge on the path of unrighteousness. This doesn't mean they were right on this issue, but it means that we have to broaden our views of orthodoxy enough to allow Christians from after Clement to before Luther to be considered saved.