I found this article written by Ryan Rufus I want to repost because he did a beautiful job of translating this difficult passage of scripture.
Philippians 2:12,13 Therefore, my dear friends, as you have always obeyed–not only in my presence, but now much more in my absence–continue to work out your salvation with fear and trembling, for it is God who works in you to will and to act in order to fulfill his good purpose.
When I was young I was taught that this passage means not to relax in your faith and feel sure that you’re going to heaven. It meant to fear the Lord’s punishment and so to live a life that’s good and honorable, never being too sure of your salvation.
However the phrase “fear and trembling” does not mean to doubt your salvation, it means “total self distrust” or “a recognition of your own weakness and inability”.
1 Corinthians 2:1-5 And so it was with me, brothers and sisters. When I came to you, I did not come with eloquence or human wisdom as I proclaimed to you the testimony about God. 2 For I resolved to know nothing while I was with you except Jesus Christ and him crucified. 3 I came to you in weakness with great fear and trembling. 4 My message and my preaching were not with wise and persuasive words, but with a demonstration of the Spirit’s power, 5 so that your faith might not rest on human wisdom, but on God’s power.
We are to live without putting our faith in our ability to be all God wants us to be and instead put our trust that God will make you into all he wants you to be. That’s why it says afterward “for it is God who works in you both to will and to do for His good pleasure”. This makes much more sense in the context of Philippians written just after he warns them against the circumcision group that wants you to be perfected according to the flesh and afterward how he makes that inspiring speech of having more credibility in the flesh than any jew and saying it was all wasted and instead he trusts in the righteousness God provides.