"So then, my beloved, just as you have always obeyed, not as in my presence only, but now much more in my absence, work out your salvation with fear and trembling; for it is God who is at work in you, both to will and to work for His good pleasure." (Philippians 2:12-13)The true mark of maturity is not how you live on Sunday, but how you live on Monday when no one from church is watching you. As parents, we teach our children how to behave through instruction and commands; watching them to ensure that their behavior lines up and conforms to what we have taught and commanded them. When they do the things we command, we praise them. When they do not, we discipline them that they might learn to follow our instructions and commands. The goal of all this is so that, when they are grown and out of our sight, they will continue to live by what we taught them and trained them to do. Our fundamental hope is that, if we "train up a child in the way he should go, [then] even when he is old he will not depart from it." (Proverbs 22:6) If we succeed in this, then we will have succeeded in raising our children to be mature adults.
Paul viewed those in the churches to which he ministered as his children. Paul wrote to the Corinthian church saying, "For if you were to have countless tutors in Christ, yet you would not have many fathers, for in Christ Jesus I became your father through the gospel." (1 Corinthians 4:15) As a father, Paul was concerned with their growth towards maturity. To this end, he desired, not only that they would obey him when present, but even in his absence, the things he taught and commanded them would continue to guide their lives, conversations, and behavior. Only when they were able to live a righteous and moral live in his absence, would he have succeeded in raising them unto maturity.
The working out of our salvation is our own personal responsibility. Having been taught and trained, it is up to us to put that training into practice. Others can instruct us, others can command us how we ought to live, but it is up to us to decide how we will actually live our lives and put to use those things we have been taught and commanded. Even the very faith we have in Christ, it is up to us to put that faith into action; to allow it to become active in our lives and to allow it to dictate and control every aspect of our daily walk and life. It is not enough to hear, learn, and understand the Gospel of God, we must actually learn to live by what we have learned, heard, and have understood. We must take what we know and put it into action.
The great paradox in all of this is that, even though we are responsible for working out our own salvation, it is not really us who are working, but God who is working within us. While our salvation is our own personal responsibility, we do not do it alone. Prior to grace, we were left to the Law and the Law commanded us what it willed but give us no help or power to do the things it commanded. We were left to our own willingness to obey and our own power to follow through on that willingness. However, now that grace has come, we are no longer left to ourselves but God Himself aids us in living the life He commands. Paul, writing of himself, speaks to our new life in Christ. "For through the Law I died to the Law, so that I might live to God. I have been crucified with Christ; and it is no longer I who live, but Christ lives in me; and the life which I now live in the flesh I live by faith in the Son of God, who loved me and gave Himself up for me." (Galatians 2:19-20) In Christ, we have died and have been given a new life. In this new life, we find that it is Christ who is living in us and who is working both to give us the willingness and the strength to live the new life we have been given and commanded. We have the very resurrected life in Christ empowering us to do the very things Paul commands; that we work out our own salvation with fear and trembling. Augustine of Hippo used to say, "Lord command what you will and grant what you command!" How great is the good news of Christ, that those things which God commands, He also gives in abundance.