St. Augustine of Hippo — the fourth- to fifth-century bishop, theologian, and philosopher — wrote about the solemnity in sermons in the late 300s and early 400s. He contrasted the gift of tongues with the chaos established in Genesis 11 when God punished humanity with separate languages for trying to construct the Tower of Babel to reach heaven.

In Sermon 271, Augustine explains that after the Flood, “the ungodly pride of men built a high tower against the Lord, and the human race was deservedly divided by languages, so that each nation would speak its own language and thus not be understood by the others.”

Augustine contrasts the pride of humanity in Genesis with “the devout humility of the faithful” who gathered together 50 days after the resurrection of Christ. At Pentecost, that humility prompted God to instill the gift of tongues to bring unity to the Church despite “the variety of their different languages,” he writes.

With this gift, the theologian explains, “the scattered members of the human race, as of one body, might be attached to their one head, Christ, and so reunited, and fused together into the unity of the holy body by the fire of love.”

“Whoever received the Holy Spirit, even as one person, started speaking all languages,” he writes. “So too now the unity itself is speaking all languages throughout all nations; and it is by being established in this unity that you have the Holy Spirit; you that do not break away in any schism from the Church of Christ which speaks all languages.”

In Sermon 267, Augustine writes that at the Pentecost, “the Church was then in one house.” He adds: “That small church spoke in the languages of all nations” and 400 years later, “this great Church now speaks in the languages of all nations from the rising of the sun to its setting.”

The growth of the Church over those four centuries, Augustine writes, is a fulfillment of God’s promise to reach across nations and languages: “You were promised to yourself: but promised in few, fulfilled in many. The Holy Spirit is the soul of the body of the Church.”

In Sermon 268, Augustine expands on how the Pentecost points to the necessity of unity in the Church under the Holy Spirit, writing that it showed “the unity of the Church in the tongues of all nations” in a small room following Christ’s resurrection. Now we see “the unity of the Catholic Church, spread throughout the whole world.”

“The duties of the members are distributed, but one spirit contains all,” he continues. “Many commands are given, many things are done: One commands, one is served. That is our spirit, that is, our soul, to our members; this is the Holy Spirit to the members of Christ, to the body of Christ, which is the Church.”