John 15:2
“Every branch in Me that bears not fruit the Father takes away.”
Here He alludes to the manner of life, showing that without works it is not possible to be in Him.
“And every branch that bears fruit, He purges it.”
That is, “causes it to enjoy great care.” Yet the root requires care rather than the branches, in being dug about, and cleared, yet about this He says nothing here, but all about the branches. Showing that He is sufficient to Himself, and that the disciples need much help from the Husbandman, although they be very excellent. Wherefore He says, “that which bears fruit, He purges it.” The one branch, because it is fruitless, cannot even remain in the Vine, but for the other, because it bears fruit, He renders it more fruitful. This, some one might assert, was said with relation also to the persecutions then coming upon them. For the “purges it,” is “prunes,” which makes the branch bear better. Whence it is shown, that persecutions rather make men stronger. Then, lest they should ask concerning whom He said these things, and lest He should throw them back into anxiety, He says,
Source: Homilies on the Gospel of John (New Advent)