Church Fathers on John 15:9

Our Lord showed above, that those who plotted against them should be burned, inasmuch as they abode not in Christ: now He shows that they themselves would be invincible, bringing forth much fruit; Herein is My Father glorified, that you bear much fruit: as if He said, If it appertains to My Father’s glory that you bring forth fruit, He will not despise His own glory. And he that brings forth fruit is Christ’s disciple: So shall you be My disciples.

The fruit of the Apostles are the Gentiles, who through their teaching were converted to the faith, and brought into subjection to the glory of God.

Made bright or glorified; the Greek word may be translated in either way. In Greek it signifies glory; not our own glory, we must remember, as if we had it of ourselves: it is of His grace that we have it; and therefore it is not our own but His glory. For from whom shall we derive our fruitfulness, but from His mercy preventing us. Wherefore He adds, As My Father has loved Me, even so love I you. This then is the source of our good works. Our good works proceed from faith…