Perseverance of the Saints

Q. Are there individuals who will experience something akin to Christian salvation and who truly believed that they were among God’s called, who nevertheless apostatize? 
A. Clearly so.  So it seems that we must admit that knowing whether one (or another) is a Christian or not can be subjectively opaque to some degree - and perhaps this is okay to admit, as such subjective opacity grounds the warning passage in Hebrews 6.

Q. Can one who is internally called by God apostatize?  
A. It seems not, but as stated in the prior question, discerning whether one is internally called can be an opaque process.

We must not confuse the doctrine of assurance with the doctrine of the perseverance of the saints.  While the latter has good grounds in the Bible, the prior is shaky - and while God’s elect cannot be lost, it’s a matter of probability on this side of heaven whether we (or others) are members of the unshakable elect.  And while God’s elect cannot lose their salvation, it seems that God can use their subjective opacity as the means of preserving them (Heb 6).  

Still, it seems that the deepest, truest, and most real type of faith, in which one personally and wholly places their trust in Jesus in a way that cannot possibly be overturned, can only be the result of election (so that no temporary believer ever possesses this type of belief).  So there is a subjective personal fruit of election that is exclusive to members of the elect alone  – and perhaps this faith can occasionally give epistemic access into something like certainty as to one’s membership in the elect.  But maybe this access is only occasional.  Assurance is flickery.

I'm unsure about my conclusions in this post.