It is clear that Paul says he is happy because Philemon was providing for the needs of the saints. For this is certain that Philemon will obey his requests since it is clear that he is of higher rank.
Nothing so shames us into giving, as to bring forward the kindnesses bestowed on others, and particularly when a man is more entitled to respect than they. And he has not said, "If you do it to others, much more to me"; but he has insinuated the same thing, though he has contrived to do it in another and a more gracious manner.
"I had joy," that is, thou hast given me confidence from the things which thou hast done to others. "And consolation," that is, we are not only gratified, but we are also comforted. For they are members of us. If then there ought to be such an agreement, that in the refreshing of any others who are in affliction, though we obtain nothing, we should be delighted on their account, as if it were one body that was benefited; much more if you shall refresh us also. And he has not said, "Because thou yieldest, and compliest," but even more vehemently and emphatically, "because the bowels of the Saints," as if it were for a darling child fondly loved by its parents, so that this love and affection shows that he also is exceedingly beloved by them.
"For we have had great joy and consolation in your love, because the hearts of the saints have been refreshed through you, brother." He emphasizes and teaches more fully why he said, "I give thanks to my God always remembering you in my prayers." It was worthy indeed to give thanks to God for the love of Philemon, who had refreshed the internal affection of the heart and the deep recesses of the saints by receiving them. And this is the apostolic idiom; to always call it "hearts," wanting to show the fullness of love in the mind. Thus, rejoicing with those who were rejoicing, and believing himself to have been refreshed with those who had rested, he has a joy not transient and light, and one that might happen by chance; but great, and as love was to Philemon, eminent, increased by the consolation descending upon Philemon's love, full of the Father of mercies and the God of all consolation.
"we have great joy". Not only, Paul says, did we rejoice, but such was the pleasure that it even brought us comfort while in bonds.
"because the hearts of the saints". See! He wishes to say: If you grant favors to others, much more grant them to me; thus he does not say; but otherwise more skillfully. For he knows the memory of benefits done to others makes those who are urged more obedient.
"have been refreshed through you". For, Paul says, they find rest in your love. They rest because of you. Since you are such a one toward the saints as to also give them rest, I have the boldness to command you. Having boldness because of Christ; to command you a fitting thing; for this is what is proper. But I said to command, not because I rule over you, but because of the love which I love you and am loved by you, I seem to command, but I do not command. For even if I appear to command you, it is out of love that I do not command but rather encourage. Thus, I do the matter with great regard. Being such a one, as Paul an elder. And I exhort, being such a one as one ought to be, he says, to persuade.
The reason he gives thanks is joy. And he says, For I had great joy and consolation... 3 John 4: ‘I have no greater joy than to hear that my children are walking in the truth.’ For this joy alleviates anxiety. That is why he adds consolation. Psalm 93:119: ‘When anxieties are increased in my heart, your comfortings delight my soul.’ He explains why, saying because through you, brother, the hearts of the saints have found rest. Colossians 3:12... ‘Put on, therefore, as God’s chosen ones, holy and beloved, a heart of mercy, kindness, humility, meekness, patience.’ 3 John 2: ‘Beloved I pray that in all things you may prosper and be in health...’
[AD 384] Ambrosiaster on Philemon 1:7