A world of difference exists between ‘work for’ and ‘work out’. Author J. Oswald Sanders draws an analogy between salvation and an estate. We do not have to feverishly work for an estate. We have already been given an estate. But we have to work it out—develop the estate’s hidden resources.
So to recap, we are saved by faith (Ephesians 2:8-9). But we need to work out our salvation with fear and trembling (Philippians 2:12).