[MurphsLaw]

If you have to work to keep your salvation, the salvation is by works, IOW, earning it.

Paul seems to think we must cooperate with God, and work on something related to salvation, or his writings make no sense ... so we have to assume he had his reasons:

... but much more in my absence, work out your own salvation with fear and trembling;
13 for God is at work in you, both to will and to work for his good pleasure.

In the same way he warns his “saved” Corinthians about abusing the Eucharist - “eating and drinking judgement upon themselves” -
again another verse, that makes no sense
if our salvation is a guaranteed deal...
Unable to be lost without Doing something.

[metmom]

Working out is not working for.