2 For these same words of the Psalter, this sweet sound, that honeyed melody, as well of the mind as of the hymn, did even beget the Monasteries. By this sound were stirred up the brethren who longed to dwell together. This verse was their trumpet. It sounded through the whole earth, and they who had been divided, were gathered together. The summons of God, the summons of the Holy Spirit, the summons of the Prophets, were not heard in Judah, yet were heard through the whole world.
They were deaf to that sound, amid whom it was sung; they were found with their ears open, of whom it was said, “They shall see him, who were not told of him; they shall understand who heard not.” Yet, most beloved, if we reflect, the very blessing has sprung from that wall of circumcision. For have all the Jews perished? And whence were the Apostles, the sons of the Prophets, the sons of the exiles? He speaks as to them who know. Whence those five hundred, who saw the Lord after His resurrection, whom the Apostle Paul commemorates? Whence those hundred and twenty, who were together in one place after the resurrection of the Lord, and His ascension into heaven, on whom when gathered into one place the Holy Spirit descended on the day of Pentecost, sent down from heaven, sent, even as He was promised? All were from thence, and they first dwelt together in unity; who sold all they had, and laid the price of their goods at the Apostles' feet, as is read in the Acts of the Apostles. And distribution was made to each one as he had need, and none called anything his own, but they had all things common. And what is “together in unity”? They had, he says, one mind and one heart God-wards. So they were the first who heard, Behold how good and how pleasant is it, that brethren dwell together. They were the first to hear, but heard it not alone....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)