"For God is my witness, how I long after you all in the tender mercies of Jesus Christ. And this I pray, that your love may abound yet more and more in knowledge and all discernment; that you may approve the things that are excellent; that you may be sincere and void of offense unto the day of Christ; being filled with the fruits of righteousness, which are through Jesus Christ, unto the glory and praise of God."
He calls not God to witness as though he should be doubted, but does this from his great affection, and his exceeding persuasion and confidence; for after saying that they had fellowship with him, he adds this also, "in the tender mercies of Christ," lest they should think that his longing for them was for this cause, and not simply for their own sake. And what mean these words, "in the tender mercies of Christ"? They stand for "according to Christ." Because you are believers, because ye love Christ, because of the love that is according to Christ. He does not say "love," but uses a still warmer expression, "the tender mercies of Christ," as though he had said, "having become as a father to you through the relationship which is in Christ." For this imparts to us bowels warm and glowing. For He gives such bowels to His true servants. "In these bowels," says He, as though one should say, "I love you with no natural bowels, but with warmer ones, namely, those of Christ." "How I long after you all." I long after all, since you are all of this nature; I am unable in words to represent to you my longing; it is therefore impossible to tell. For this cause I leave it to God, whose range is in the heart, to know this. Now had he been flattering them, he would not have called God to witness, for this cannot be done without peril.
And not merely upright, but "filled with the fruits of righteousness." For there is indeed a righteousness not according to Christ, as, for example, a moral life. "Which are through Jesus Christ to the glory and praise of God." Do you see that I speak not of my own glory, but the righteousness of God; and oftentimes he calls mercy itself too righteousness; let not your love, he says, indirectly injure you, by hindering your perception of things profitable, and take heed lest you fall through your love to any one. For I would indeed that your love should be increased, but not so that you should be injured by it. And I would not that it should be simply of prejudice, but upon proof whether I speak well or no. He says not, that you may take up my opinion, but that you may "prove" it. He does not say outright, join not yourself to this or that man, but, I would that your love should have respect to what is profitable, not that you should be void of understanding. For it is a foolish thing if you work not righteousness for Christ's sake and through Him. Mark the words, "through Him." Does he then use God as a mere assistant? Away with the thought. Not that I may receive praise, says he, but that God may be glorified.
Along with good teaching he prays that they might have an upright life, and not simply upright but truly filled with the fruits of righteousness. He is not speaking here of a kind of uprightness or virtue that tries despairingly to grow without Christ.
[AD 407] John Chrysostom on Philippians 1:8-11
He calls not God to witness as though he should be doubted, but does this from his great affection, and his exceeding persuasion and confidence; for after saying that they had fellowship with him, he adds this also, "in the tender mercies of Christ," lest they should think that his longing for them was for this cause, and not simply for their own sake. And what mean these words, "in the tender mercies of Christ"? They stand for "according to Christ." Because you are believers, because ye love Christ, because of the love that is according to Christ. He does not say "love," but uses a still warmer expression, "the tender mercies of Christ," as though he had said, "having become as a father to you through the relationship which is in Christ." For this imparts to us bowels warm and glowing. For He gives such bowels to His true servants. "In these bowels," says He, as though one should say, "I love you with no natural bowels, but with warmer ones, namely, those of Christ." "How I long after you all." I long after all, since you are all of this nature; I am unable in words to represent to you my longing; it is therefore impossible to tell. For this cause I leave it to God, whose range is in the heart, to know this. Now had he been flattering them, he would not have called God to witness, for this cannot be done without peril.