Heres my take:
But I keep under my body, and bring [it] into subjection: lest that by any means, when I have preached to others, I myself should be a castaway.
1 cor 9:27
Wherefore, my beloved, as ye have always obeyed, not as in my presence only, but now much more in my absence, work out your own salvation with fear and trembling.
Philippians 2:12
I have heard folks/preachers state that they are 100% sure of salvation, and I get that. But I look at it a little differently.
I am 100% confident in Jesus' sacrifice for sin. What I am not so confident in is my ability to stay "In Christ" . According to the scripture above, Paul wasn't too confident either! I know I am saved as long as I stay on the path. But I will not act as if it's a done deal. His act is done....mine isn't until I take my last breath on this Earth. At that point hopefully I can say that I have fought a good fight I have kept the faith!