I don't understand sacrementals like the Brown Scapular, Promises of the Rosary, etc. It seems like they go against the RC belief that no one can know whether they will be saved.
From the promises attached to the Sacred Heart devotion:
In the excessive mercy of His Heart that His all-powerful love will grant to all those who receive Holy Communion on the First Fridays in nine consecutive months the grace of final perseverance; they shall not die in His disgrace, nor without receiving their sacraments. His divine Heart shall be their safe refuge in this last moment.http://www.fisheaters.com/sh.html
This sounds pretty all-encompassing to me. For those who complete the devotion. I don't see how it differs from Protestant beliefs in the Perseverance of the Saints.
I've been wondering the same thing, mostly because many Catholics/Orthodox tend to create a straw-man with Eternal Security (though in their defense, many proponents of eternal security don't really know what they're saying).
As I've always been taught, we're justified and then begin the process of sanctification. This doesn't mean we say a prayer and we're done. Instead, it's always said that works serve as proof for faith, that someone without works is someone without faith.
I think where the Orthodox differ is they teach it's possible for one to have works because of faith, but they can abandon the faith and turn against God. Many Protestants believe that one can "backslide" against God, but one will always be justified, regardless of actions (though the hypothetical, "well maybe he wasn't really saved" is offered).
To me, this is one of the hardest beliefs to get over because ever since I was a child it's been ingrained into my head that we're justified and then begin the process of sanctification. To believe any different is wrong, heretical, and causes you to go to Hell since you're denying the mercy of Christ (this is what I was taught...I certainly don't believe that denying it is cause to go to Hell, but there is a major psychological impact from growing up hearing that).