Calvin fought to bring the Bible out of the RCC closet. Paul warns against back sliding, but the Bible doesn’t teach that one who is born again can be un-born. The word “salvation” does not alway mean the same thing as conversion. As with nearly every single word, the context reveals its meaning. There is a present tense of being saved that Paul is describing - being saved from today as we run the race, having been saved upon conversion so that we could run.
“God’s workings are not limited to our ability to comprehend.” You and I can agree on this point.
Why would Paul, who I would think would meet the definition of "saved" need to keep running the race? Persevere for what? One only needs to preserver until the end of something. Eternal salvation is true, true and true, but only after the racers have run and they have persevered until the end that is death. That is the point at which salvation becomes eternal, that is the point of perseverance, that is when our Lord will say "well done my good and faithful servant!", I was saved at my baptism, I am being saved as I persevere and I will be saved at my death if I have persevered through His grace to the end of the race.