My friend - if it were a “one time event”, then we would all have to believe in “eternal security” like our calvinist brothers (still brothers though we disagree) and it would render void the many verses (such as the OP reference to work out our salvation in fear and trembling; and paul’s hope to “persevere” and “finish the race” and render void Pauls’ warning about Gentile believers (saved) being grafted out of the root) and render void verses that tell us its worse to “know the truth” (salvation) and fall away, then to never have known it all - and to render void Jesus warning that many who called upon his name (some of whom cast out demons in his name - power of the Holy Spirit per Jesus’ words, not power of demons) would be “goats” based upon what they did not do for the poor and hungry and would be cast out.
No - justification, like sanctification, is an ongoing process - this is what scripture teaches us and the “once saved only saved doctrine” is a dangerous trap, I fear, for the unwary.
Blessings,
Brian