12 Therefore, 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; 13 for it is God who works in you both to will and to do for His good pleasure. 14 Do all things without complaining and disputing, 15 that you may become blameless and harmless, children of God without fault in the midst of a crooked and perverse generation, among whom you shine as lights in the world, 16 holding fast the word of life, so that I may rejoice in the day of Christ that I have not run in vain or labored in vain.
St. John Chrysostom in his Homily VIII on Philippians II said:
“The admonitions we give ought to be accompanied by commendations, for so they even become welcome, when we refer those whom we admonish to that measure of zeal which they have themselves exhibited, as Paul, for instance did here; and observe with what singular discretion …And why ‘much more in my absence?’ You seemed perhaps at that time to be doing everything out of respect to me, and from a principle of shame, but that is no longer so. If you make it evident that you now strive more earnestly, it is also made evident that neither was it done out of consideration to me then, but for God’s sake…”
“‘Work out your salvation with fear and trembling’… Paul had such fear: and therefore he said, I fear ‘lest having preached to others, I myself should be rejected’ (ICor.9:27) …So much of fear is necessary merely in order that we may master the indolence natural to us. Where there is so fierce a war and such great hindrances, how can we by any possibility be saved without fear? And how may this fear be produced? If we only consider that God is everywhere present, hears all things, sees all things, not only whatsoever is done and said, but also all that is in the heart, and in the depth of the soul, for He is ‘quick to discern the thoughts and intents of the heart’ (Heb.4:12), if we so dispose ourselves, we will not do or say or imagine anything that is evil… Never despise His patient endurance, for it is to bring you to repentance that He is longsuffering. Whenever you eat, consider that God is present, for He is present; whenever you are preparing to sleep, or giving way to passion, if you are robbing another, or indulging in luxury, or whatever you are about, you will never fall into laughter, never be inflamed with rage. If this is your thought continually, you will continually be in ‘fear and trembling.’ ‘Serve the Lord with fear and rejoice unto Him with trembling’ (Ps. 2:11).”
Augustine the Blessed in his Sermon 81 on the New Testament said:
“…when Christ Crucified is preached, two hear, one despises, the other ascends. Let him that despises, impute it to himself; let not him that ascends arrogate it to himself. For he has heard from the True Master; ‘No man comes unto Me, except it were given unto him of My Father.’ Let him joy, that it has been given; let him render thanks to Him who gives it, with a humble, not an arrogant heart; lest what he has attained through humility, he lose through pride. For even they who are already walking in this way of righteousness, if they attribute it to themselves, and to their own strength, perish out of it. And therefore Holy Scripture teaching us humility says by the Apostle, ‘Work out your own salvation with fear and trembling.’ And lest hereupon they should attribute ought to themselves, because he said, ‘Work,’ he subjoined immediately, ‘For it is God who works in you both to will and to do of His good pleasure.’ ‘It is God who works in you;’ therefore ‘with fear and trembling,’ make a valley, receive the rain. Low grounds are filled, high grounds are dried up. Grace is rain. Why do you marvel then, if ‘God resist the proud, and gives grace unto the lowly’? Therefore, ‘with fear and trembling;’ that is, with humility. ‘Be not high-minded, but fear.’ Fear that you may be filled; be not high-minded, lest you be dried up.’