And, I think this is where I would have an honest disagreement with Catholics, and I'm not sure about you yet Kosta. :) I would say God never leaves His elect, EVER! This is true even when the elect choose to disobey temporarily (if the choice is permanent, then God was never present in the first place so He couldn't have "left"). Because I believe He never leaves, I can't accept that salvation is won or lost based on the instant of confession and the first mortal sin thereafter.
This disagrees with the Scripture that tells us that those who are Baptised have received the Holy Spirit and the first installment of salvation - and yet - some people become disinherited from the Kingdom as a result of serious sins, sins that John calls "deadly". Why does John consider that Christians can sin deadly if 1) Christ was never there to begin with or 2) We can not die if we are of the elect from our point of view? Your view would have Christ NEVER within the Christian - which is patently false.
Please remember that the elect cannot be left out of heaven IN THE END - but who is to say that God doesn't leave that person for a time? Recall the Prodigal Son. Was the father with the son when he went on his little "excursion" through sin and dissipation? The point is that God KNOWS that the Elect will RETURN! Nothing about not leaving or how rocky the journey will be.
Of course, WE don't know if we are of the elect to begin with, so all of this talk about assuredness is a bit presumptuous for me.
Regards