Philippians 4:12
Wherefore, my beloved, as you have always obeyed, not as in my presence only, but now, much more in my absence, work out your own salvation with fear and trembling
I think that sometimes we need to take a fresh look at salvation and all that is involved in it. We know that salvation is by grace through faith. It is also the free gift of God that no man can earn by works or deeds. (Eph. 2:8-9) If salvation is a free gift that is not earned or deserved, then why does this verse say that we are to work out our salvation? It sounds like it is saying that we have to work for our salvation. I know that there are some who teach and believe that.
The problem with that teaching is that it contradicts all the rest of scripture. You will not find in any other context the idea that you have to work to earn your salvation, but you will find all throughout the Bible the teaching of the free gift of salvation. One of the rules of Biblical interpretation is to interpret a scripture by the rest of the scriptures. The Bible is the best commentary available on itself.
If this is the case then there seems to be a disagreement in the scriptures. This perceived contradiction is only in interpretation. You see a better translation of this verse would be for us to continue to walk out our salvation on a day to day basis until the the time when we go to be with the Lord. It is in the context of a contract that is between two people and one decides to get out of the contract. In that case you would encourage that one to continue to work out the full term of the contract and not to stop halfway.
This is what Paul is saying here. He is saying that even though he is absent from them, that they are to continue to serve out their salvation contract. You see, when we become a Christian, we declare Jesus our Lord or boss and we are under agreement to serve Him for the rest of our lives. Not working for our salvation, but working because of our salvation.