It was speaking, opposed to being silent (1 Corinthians 14:28), yet
not always in a foreign tongue. On the day of Pentecost the Apostles did indeed speak the various languages of their hearers, but the still unbaptized Gentiles in the house of Cornelius “speaking with tongues, and magnifying God” (Acts 10:46) and the twelve newly baptized Ephesians speaking with tongues and prophesying (Acts 19:6) had no reason for using any strange tongue. Again, instead of the expression “speaking with tongues” Paul uses the alternative phrases, “speaking in a tongue”, “by a tongue”, “with a tongue” (1 Corinthians 14:2, 4, 13, 14, 27). The object of the gift was not to convey ideas to listeners, but to speak to God in prayer (ibid., 2, 4), an object for which a foreign language is unnecessary. Lastly — and this argument seems conclusive — Paul compares glossolalia, as regards its effect, with talking in an unknown language; it is, therefore, not itself an unknown language (ibid., 11).
It was an articulate language, for the speaker prays, sings, gives thanks (ibid., 14-17).
The speaker was in a kind of trance — “If I pray in a tongue, my spirit [pneuma] prayeth, but my understanding [nous, mens] is without fruit” (ibid., 14).
on unbelievers glossolalia made the impression of the marvellous; perhaps it recalled to their mind the religious ravings of hierophants: “Wherefore (i.e. because unintelligible) tongues are for a sign, not to believers, but to unbelievers. If . . . all speak with tongues, and there come in unlearned persons or infidels, will they not say that you are mad?” (1 Corinthians 14:22, 23).
The gift of tongues is inferior to that of prophecy: “Greater is he that prophesieth, than he that speaketh with tongues: unless perhaps he interpret, that the church may receive edification” (ibid., 5).
The charisma of interpretation is, then, the necessary complement of glossolalia; when interpretation is not forthcoming, the speaker with tongues shall hold his peace (ibid., 13, 27, 28). Interpretation is the work either of the speaker himself or of another (ibid., 27). It takes the form of an intelligible address; the explanation was to follow the speech with tongues as regularly as the discerning of spirits succeeded prophecy (1 Corinthians 14:28, 29).
Among the Fathers it is sententia communissima that the speaking with tongues was a speaking in foreign languages. Their interpretation is based upon the promise in Mark 16:1, “They shall speak with new tongues”, and on its final fulfilment in the gift of tongues to the apostles (Acts 2:4). A new tongue, however, is not necessarily a foreign language, and a gift which had a special use on the day of Pentecost appears purposeless in meetings of people of one language. There are, besides, textual objections to the common opinion, although, it must be owned, not quite convincing [see the second point above]. Many explanations of this obscure charisma are proposed, but not one of them is free from objection. It may indeed be that there is some truth in all of them. St. Paul speaks of “kinds of tongues”, which may imply that glossolalia manifested itself in many forms: e.g. in the form of foreign languages when required by circumstances, as with the Apostles; as a new language — “a kind of speech distinctive of the spiritual life and distinguished from common speech, which to the exuberant feeling of the new faith appeared unsuitable for intercourse with God” (Weizsacker); or as the manifestation of the unspeakable groanings of the Spirit, asking for us, and causing us to cry, “Abba, Father” (Romans 8:15, 26).
I did know the Corinthians were being a little problematic and this is the reason Paul notes the need for ‘edification.’