Life refers to graceHi Don,
We can know that we are saved now if we are disciples of Christ and adhere to His teachings, which are many.
I do believe you're correct that we cannot be absolutely certain of our salvation till the end of our life for the reason you've stated above...
Matthew 24:13 we will be saved if we endure till the end.
However, don't you believe you can know, at the foot of the cross, that you are saved right now?
John 10:10 states that Jesus came to give us a life more abundant.
It cannot be abundant if we cannot know we are saved right now...
(the future we cannot know because we might fall away).
We are in Christ and filled with grace and have eternal life but we must continue to believe and abide in Him Jn15:4 to the end Matt 24:13
Thanks