How would one ever know in this lifetime? The Protestant side seems to not believe that any one of them could be wrong. Being a Protestant is really very attractive from the human point of view. It is a real miracle more people are not Protestant. First, Protestants believe that Christ died for all their sins, past, present and future, so the bill is paid in full; they owe nothing.
Second, you are absolutely sure that the Holy Spirit indwells you and guides you. The fact that they all believe in a slightly different set of beliefs is irrelevant by all indications. By adopting Jesus as their Savior, they are justified in the yes of God, their sins have been wiped off, yesterday, today and tomorrow, and they are basically 'saved.'
Third, if they sin, Christ has already paid for them, so you really can't rack up any spiritual "debt" by sinning. Although it may not be something they desire or necessarily like, sin is a fact of life and truly very little of real concern as far as their already established state of 'salvation.'
Fourth, once you have convinced yourself that you are guided by the Holy Spirit, you are sure that He will never leave you. So, the peace of mind is right there along with imputed self-righteousness.
Thus, guided by the Holy Spirit, you create a personal faith and become your own "pope." If you don't like the First Baptist Church on Main Street, because the pastor teaches free will, or rapture, you can always go to the First Baptist Church on east Avenue and still be a Baptist...or whatever other flavor of Protestant you identify yourself with. Or, you can become a "non-denominational"
If you don't like the creed your church uses, you can always write another one. If you consider yourself Reformed, there is no hard and fast rule as to just how much concordance there must be between you and the other Reformed.
So, to pout it simply, it's cozey, it's easy and it's rather well tailored to man's nature lookign at it from outside.
Now, in all fairness, I don't know if that is how it is, but not a single one could prove to me that he or she is guided by the Holy Spirit, nor can any of them explain how is it that they all believe slightly different things if they are all taught by the same Teacher?
To an outsider, it seems terirbly presuptious, arrogant and conaceited. But, the various Protestants will tell me that I am dead wrong on this. And I would like to believe them, because most of them seem to be very decent and God-fearing people, but they have yet to explain all this in a way I can understand. Being absolutely sure they are saved and guided by the Holy Spirit does not contain even a slight possibility of error on thier part.
On that question I was referring to if anyone "lost their assurance." You know, if someone was assured and then later - in this lifetime - wasn't assured anymore - doubted their assurance or lost it completely.
Or if externally.. One says he is "assured" and others of the same church say, "ain't no way in hell that guy is saved.." Something like that. Whether there was a logical requirement of Once Assured Always Assured.
I would imagine there has to be some cases of people losing their assurance.
As to the attraction of personal theology of Reformed, I think it also appeals to the individualism of the West - the frontierism and the conjunction of revolt and self-rule, democracy. I often see the argument made that the nation's founders were Calvinist, or the something similar.
And there is also a variation of sins "wiped off" where sins are "covered over." Add to this, the range of predeterminism and the theological permutations become multiplied again.
Nondenominationalism is the rage in many places and then there's the prosperity Christianity, believe to receive, that I think most Protestants here recognize as secular peversion of the beatitudes.
It may sound contrary, but sometimes I see Protestant Churches as talking one aspect of Catholocism, eliminating the rest and expanding on their chosen piece. The only piece never picked is monasticism.
thanks for your reply, perhaps a Protestant will speak to the question of Assurance of assurance...
And this is the sad bottom line in all of this.