Why did Peter quote these verses from Joel? Because everyone was speaking in tongues.
'And they were all filled with the Holy Ghost,
and began to speak with other tongues,
as the Spirit gave them utterance.
And there were dwelling at Jerusalem Jews, devout men, out of every nation under heaven.
Now when this was noised abroad, the multitude came together, and were confounded,
because that every man heard them speak in his own language.
And they were all amazed and marvelled, saying one to another,
Behold, are not all these which speak Galilaeans?
And how hear we every man in our own tongue, wherein we were born?
Parthians, and Medes, and Elamites, and the dwellers in Mesopotamia,
and in Judaea, and Cappadocia, in Pontus, and Asia,
Phrygia, and Pamphylia, in Egypt, and in the parts of Libya about Cyrene,
and strangers of Rome, Jews and proselytes, Cretes and Arabians,
we do hear them speak in our tongues the wonderful works of God.
And they were all amazed, and were in doubt, saying one to another,
What meaneth this?
Others mocking said, These men are full of new wine.'
Why were the disciples speaking in tongues?
* Because, in the words of those who heard, 'We do hear them speak in our tongues the wonderful works of God'.
God wanted everyone to hear what He had to tell them, and that necessitated that they speak in the languages of those who were present at that time.
* The response of Peter, was to the question, 'What meaneth this?
" and the mocking of those who asserted that they were all, 'full of new wine',
not to the tongue speaking itself. The tongue speaking was only the means to an end. It also gave audio witness to the fact that a work of God had taken place, as is seen in Acts 10:45.
* It is also spoken of as indicative of spiritual childhood, and not of full growth. (1 Corinthians 13:12-13).
'Charity never faileth:
but whether there be prophecies, they shall fail;
whether there be tongues, they shall cease;
whether there be knowledge, it shall vanish away.
For we know in part, and we prophesy in part.
But when that which is perfect is come,
then that which is in part shall be done away.
When I was a child, I spake as a child, I understood as a child, I thought as a child:
but when I became a man, I put away childish things.'
'And now abideth faith, hope, charity, these three;
but the greatest of these is charity.'
In Christ Jesus