Really didn't mean to derail this thread, but it is your thread and you seem genuinely concerned so here goes.
First, let me just reassure you. There is one and only one way God imparts the grace of salvation upon someone... and that is when they believe and confess Christ. That's it. There is no good deed you could ever do that would add anything to that. (Not to say good deeds don't have their place but that's another discussion).
Conversely, there is no bad deed you could ever do that would take salvation away. Since it hinges on belief and confession, bad deeds do not erase God's grace. (Not to say that bad deeds don't have their place, but that's yet another discussion).
Believe and confess. You're in. Dis-believe and deny and you're out.
I hope that helps calm your nerves and give you a litmus test by which to judge your real position.
Now, the Bible seems to be at odds with itself on the subject. There are verses that say once His God will never let us go, yet there are also passages that clearly say there are those who will taste God's grace and turn away. And that stickler of 'they were never with us' of those who do. The basic arguments are, can one fall out of a tree they never climbed into, and if one climbs that tree and falls out of it, were they really ever in the tree to begin with?
Most people play one set of verses against the other, thus the endless debate. Me, I think how can these opposites be really both true?
Whiiich brings us back to your question of time travel. I believe God has access to all of time, all of the time (yet another discussion). I also believe that God's knowing everything that's going to happen, doesn't mean He causes those things to happen. So, He watches Joe go to church and come to believe, and God writes Joe's name in the book of life. Joe after many years backslides, falling deeper and deeper into sin. No matter how deep Joe sinks he's still saved - until that point satan puts him in a position of having to confirm his faith. Joe then abandons belief and denies Christ.
God then goes back in 'our time' and erases Joe's name from the Book, making to be as if it were never there from the beginning.
Time goes on and eventually we'll meet our maker and the Book will be opened. Joe's name won't be there, just as if it never was. But clearly, in our time line at least, it was at one point there.
Take a breath. Remember you asked for this
OK, Peter denied Christ. 3 times to be exact. But
he never stopped believing in Him. That's part of the equation. Joe stopped believing. That's the difference between backsliding and apostasy. One is not walking the walk. The other is denying there IS a Walk.
Hope that helps
