John 15:8
“Herein is My Father glorified, that you be My disciples, and bear much fruit.”
Hence He makes His discourse credible, for if the bearing fruit pertains to the glory of the Father, He will not neglect His own glory. “And you shall be My disciples.” Do you see how he that bears fruit, he is the disciple? But what is, “In this is the Father glorified”? “He rejoices when you abide in Me, when you bear fruit.”
Source: Homilies on the Gospel of John (New Advent)