And they were all filled with the Holy Spirit, and began to speak with other tongues, as the Spirit gave them utterance.
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Cyril of Jerusalem
And they began to speak in various languages:
The Galilean Peter or Andrew spoke Persian or Median. John and the rest of the Apostles spoke every tongue to those of Gentile extraction; The Holy Spirit taught them many languages at once, languages which in all their life they never knew. This is in truth vast wisdom, this is power divine. What a contrast of their long ignorance in time past to their sudden, complete and varied and unaccustomed exercise of these languages! ...
Began to speak divers tongues. Perhaps the apostles spoke only their own tongue, and the miracle consisted in each one's understanding it as if they spoke it in his language. (St. Gregory of Nazianzus, orat. xliv.)
But St. Augustine and most others, understand the text literally; though the apostles had not this gift on all occasions, nor on all subjects, and therefore sometimes stood in need of interpreters. See St. Augustine, in Psalm xvii.; Expos. 2.; and Serm. 188.
The same Father observes, that the conversion of all nations to the Church, and their being united in one faith, all having one language or confession, is a perpetuation of the same miracle in the Church. ...
But after ten days from the ascension, which from the first Lord's day is the fiftieth day, do ye keep a great festival: for on that day, at the third hour, the Lord Jesus sent on us the gift of the Holy Spirit, and we were filled with His energy, and we "spake with new tongues, as that Spirit did suggest to us; " ...