It is as though he says: how desirable your firmness in the faith was, and how I feared for it. The news surpassed my expectations. This is a great benefaction of God for me. I have no strength to thank God worthily for this good.
My joy because of you has no measure. St. Chrysostom says: “Expanding what was said above, that is, ‘we live,’ the Apostle says: ‘For what thanksgiving can we render?’
“You were the cause for us of such great joy that we are unable to thank God worthily. We consider your success a gift of God. You have benefited us so greatly that we consider it a work accomplished by God’s inspiration, or rather, the work of God Himself.
“Such exalted dispositions are not the work of human efforts.”
“Can we render.” One renders a debt. Considering himself greatly benefited, he feels obliged to thank God, yet finds no strength to thank Him worthily. So great is the good of being gladdened.
“The greatness of the rejoicing overcomes the hymnody of the lips. For we are unable to raise to God a song equal to the joy that has been given us by you” (Theodoret).
“Concerning you.” He speaks only of his joy because of them, as an expression of his strong and irrepressible love for them.
“For all the joy” either indicates the various things that gave joy, or generally signifies the fullness of joy. Thus it means: for all this joy. To this also belongs “with which we rejoice for your sake.”
“To rejoice with joy” means to rejoice fully, in the highest degree. It is the same as elsewhere, “to rejoice with great joy” (Mt 2:10).
“Before God.” This elevates the value of the joy. He rejoices with such joy as is proper before God, a holy and reverent joy, conceived and maturing in the spirit of faith and devotion to God.
Here too is assurance of the sincerity of his joy, as though he said: before God, the all-seeing witness of everything that happens secretly within.