"Wherefore, my beloved, as ye 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. For it is God which worketh in you both to will and to do of his good pleasure." (Phi 2:12-13)
"So that, my beloved, as ye always obey, not as in my presence only, but now much more in my absence, with fear and trembling your own salvation work out, for God it is who is working in you both to will and to work for His good pleasure." (Phi 2:12-13 YLT)
The KJV divides this passage into two verses 12 and 13, but it really is all one long sentence like in Young's literal translation. Paul's writing is like that. He has these long, run-on sentences that are sometimes difficult to translate. The word translated "work out" is literally "fully work" and has the sense of an on-going act that leads to completion. One use of this word was to refer to mining. To "work out" the mine means to get everything possible out of the mine. This same word is translated as "having done" in Ephesians 6:13, but would literally be "having fully worked". It is also used in James 1:3 as, "faith worketh patience" and represents that patience is the full-working-out of faith. Probably "accomplish" would be a good word in English to convey the same thing.
The CEV paraphrase is:
"My dear friends, you always obeyed when I was with you. Now that I am away, you should obey even more. So work with fear and trembling to discover what it really means to be saved. God is working in you to make you willing and able to obey him.