Philippians 2.12 - 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...
This verse follows very much on the heels of Paul's challenge to the church to receive God's grace and extend it to one another through living in unity, not living selfishly, but putting others before ourselves - just as Christ did! So, on the back of the example of Christ that we are to follow comes this "therefore", calling us to work out (or live out) the salvation we've received.
There are a couple of pieces of this that I find particularly striking:
First, Paul acknowledges the choice of the church to live in obedience whether he was there with them or not (and really, living even more in obedience in his absence). What a commendation to the church he was writing to. For me, this raises the question, what do we do when nobody is looking? When there is nobody checking up on us or closely monitoring our actions, what do we choose to do? Do we act with integrity even though it might not be noticed? For Paul, if we're following the example of Jesus, then our integrity is not bound to whether someone is watching or not.
Second, the idea that working (or living) out our salvation is something we're to do with fear and trembling, and that really involves what Paul has been talking about already. This is not a way to earn our salvation back or make sure that we've paid enough for it - after all, Jesus paid the whole cost - but rather living out what that salvation is about. Again, this means living out the example of Christ as we live in unity and love with one another, and that is done in the little decisions made everyday: choices for blessing rather than selfish gain, unity instead of division, peace instead of grumbling.
After all, it's the little things that count!