Let me ask you a question.
How can so many believer's extrapolate different ideas when they are all talking to the same spirit.
If I told you that I am the only one who possesses the true spirit & the right theology, would you laugh in my face? (Maybe a little) But you can't prove that I don't, just like no one here can prove you dont, just like you can't prove they don't.
It all comes down to opinion, doesn't it.
I've asked that many times.
I do feel that we have to, after our own investigation, stick to some kind of traditional theology --- whatever that may mean; it could mean different things to different persons.
One problem I have with Protestantism is this idea that we're all little theologians and can come up with our own "opinions".
OTOH, I came out of the CC and we were told that it's the one true church and everything it teaches is correct. So when I decided to leave it I had to study up a bit on my own to make sure I was making the right decision...or at least felt I was making the right decision.
The next church I attended, Nazarene, agreed with the CC on many ideas so this was good for me.
Surely you must be referring to what is being addressed in this thread:
1. Eternal Security.
Some believe it's from God. Like Calvinists. So, you're right, how could anyone ever be sure of their salvation if they have nothing to do with it.
Some believe it's up to us to continue in our faith and worship of God to maintain this salvation...I believe this. I get scolded for saying we have to obey God, but that's what the N.T. tells me. Some think faith is ALL that is necessary.
Some believe that once we savor the love of God it becomes impossible to leave that love that He has for us and if they do it means they were never saved to begin with. (or they never would have left).
How can we know who is right? Two churches I attended agreed with no. 2, the middle paragraph. I see in the N.T. words such as IF, CONTINUE IN, RUN THE RACE, ENDURE TO THE END, KEEP THE FAITH, etc. This shows me that indeed the second paragraph is the right way to go or all these warnings would not be in the N.T.
2. Covenants
I don't know how others know the covenants, but I had to study them so I could teach them to others. I had to go outside of the bible and read theological writings. There is much to know regarding this and I'm aware that I know very little due to the volumes that is written about each covenant. So, even here I'm going by theologians writings, not my own opinions.
Opinions should not have a place in our faith. OTOH, we do need to consciously agree with what we are being taught since we will be judged by what we know on an individual basis.
Complicated subject, I guess.