The question of predestination is one of an intricacy disproportionate to its interest, to paraphrase Chief Justice John Marshall, or at least its relevance to us on earth in leading our lives (interesting phrase, by the way: leading a life instead of, say, living it).
What I mean is that we cannot be so sure of the answer — so sure about whether or not our eternity is predestined so that our efforts here on earth don’t matter — that it would make rational a failure to try our best to act as God would want. If asked whether one believes in predestination, it is bad advice to say other than, “I can give you my opinion of what the Bible means, but I can’t be 100 percent certain, and my opinion will in any event not tell you that you should not act as God says we should act elsewhere in scripture.”
The calculus here is very similar to Pascal’s wager, is it not? You have, again, four possible quadrants/outcomes, and acting as if there is no predestination can have a huge payoff and avoid a huge loss, with relatively little opportunity cost compared to acting as if there is predestination.
This is true elsewhere in the Bible, by the way. That is, it can be foolish to rely too much, if we don’t have to, on what can only be an uncertain interpretation of the text — and the less of the text there is, the more foolish the reliance.
P.S. I think a similar approach makes sense in addressing whether salvation (via faith) can be lost (via loss of faith). If there are arguments on both sides, it is only prudent to make every effort to avoid losing faith and to do what one can to keep other people from losing their faith as well. Sure, one can think of situations where the loss of faith due to a passing moment of weakness is implausible, but also situations where a moment of fleeting belief — perhaps by a third grader during Sunday school, followed by a lifetime of unrepentant sin and rejection of God — is hard to envision as a saving faith. God’s existence outside of time only complicates matters. So continue to nourish and pray for your faith and the faith of others.