Unspeakable joy

John　15:26-16:4

Jesus calls the Holy Spirit the Advocate, a name taken from His office from Isaiah 9:6, completing the revelation of the Trinity. The Holy Spirit not only relieves the sorrows of the faithful, but fills them with unspeakable joy. Everlasting gladness is in those hearts, in which the Spirit dwells.

But what evil was it to the Apostles to be put out of the Jewish synagogues? Our Lord wished to make known to them, that the Jews were about not to receive Him, while they on the other hand were not going to desert Him. The meaning of the words is this: They shall put you out of the synagogue, but do not be afraid of being left alone. Separated from their assemblies, you shall assemble so many in my name, that they, fearing that the temple and rites of the old law will be deserted, will kill you and think to do God service thereby, having a zeal for God but not according to knowledge.

See:
St. Augustine (Tractates on the Gospel of St. John, Tractate #93)
Didymus the Blind (On the Holy Spirit)