That believers would one day be given the supernatural utterance in other languages unknown to the speaker was not only prophesied by Jesus; Mark. 16:17; but also by Isaiah. 28:11. This prophesied gift of the Holy Spirit came to pass as we know on the day of Pentecost.
4. And they were all filled with the Holy Ghost, and began to speak with other tongues, as
the Spirit gave them utterance.
Also Acts. 10:46; 19:6; The Apostle Paul goes into lengthy detail explaining this gift along with all the gifts of the Holy Spirit to the Church in Corinth. 1Corinthians. 12:10, 28:31; 13:1- 3; 14:2, 4- 22, 27- 32.
From 1 Corinthians. 13.1; It would be evident as most believers would know that there are both the languages or tongues of man as displayed in Acts 2:4; the purpose of which I would suppose is for spreading the Gospel of Jesus Christ amongst peoples of different nationalities and Angelic tongues, the tongues of Angels. The reason for this kind of utterance I can only put down to Romans. 8:26. I know myself at times I do not know what to pray for, in this day there are so many needs I feel at a loss as to where to start at times or I will lose concentration. Most of us including yours truly will tend to be some what a little self centered in prayer. This utterance when moved by the Holy Spirit I feel is praying in an area or situation that God want's to move.
26. Likewise the Spirit also helpeth our infirmities: for we know not what we should pray
for as we ought: but the Spirit itself maketh intercession for us with groanings which cannot be uttered.
As stated by the Apostle Paul in I Corinthians. 14; as noted above.
2. For he that speaketh in an unknown tongue speaketh not unto men, but unto God: for no man understandeth him; howbeit in the spirit he speaketh mysteries.
I am also aware that an utterance in tongues by a speaker when moved by the Holy Spirit can give a word of knowledge, a word of encouragement to an individual or a Church body when there is one or more to interpret. Prophecy can also be given through the utterance in tongues as the following verses from 1 Corinthians tell us.
6. Now, brethren, if I come unto you speaking with tongues, what shall I profit you, except I shall speak to you either by revelation, or by knowledge, or by prophesying, or by doctrine?
13. Wherefore let him that speaketh in an unknown tongue pray that he may interpret.
Pray and pray we must, that we may interpret for the edification of the body of Christ.
26. How is it then, brethren? when ye come together, every one of you hath a psalm, hath a doctrine, hath a tongue, hath a revelation, hath an interpretation. Let all things be done unto edifying.
27.If any man speak in an unknown tongue, let it be by two, or at the most by three, and that by course; and let one interpret.