Paul calls us to “work out” our salvation for it is God who “works in” us.  Notice the parallel in these phrases.  We have our own contribution to make in the unfolding of our salvation, and God has a part to work in you.  

Note, Paul does not say we work for our salvation, but that we work out our

Read: Ephesians 2:8-9

Paul’s use of the phrase “work out your salvation” can be compared to working out.  We already have our salvation through our faith in Christ.  We are not working to gain salvation.  Just like in working out, you are not creating a new muscle that hadn’t existed in your body before, you are strengthening the muscles that God had already given you.  So it is with this verse.  We are not working for salvation that didn’t exist, we are strengthening ourselves as Christians - we are building our “Christian muscles!