Paul is encouraging us, in view of who Jesus is and what He’s done for us, to press on in our pursuit to live out our salvation. We’ll discover that this is not an endless requirement to do good works, but is rather a call to respond and participate by aligning our will with God’s, as His new creation in Christ.
Therefore, my beloved, as you have always obeyed, so now, not only as in my presence but much more in my absence, work out your own salvation with fear and trembling, for it is God who works in you, both to will and to work for his good pleasure.