Acts 2
5 And there were dwelling in Jerusalem Jews, devout men, from every nation under heaven.
6 And when this sound occurred, the multitude came together, and were confused, because everyone heard them speak in his own language.
7 Then they were all amazed and marveled, saying to one another, “Look, are not all these who speak Galileans?
8 And how is it that we hear, each in our own language in which we were born?
9 Parthians and Medes and Elamites, those dwelling in Mesopotamia, Judea and Cappadocia, Pontus and Asia,
10 Phrygia and Pamphylia, Egypt and the parts of Libya adjoining Cyrene, visitors from Rome, both Jews and proselytes,
11 Cretans and Arabs—we hear them speaking in our own tongues the wonderful works of God.”
12 So they were all amazed and perplexed, saying to one another, “Whatever could this mean?”
13 Others mocking said, “They are full of new wine.”
The tongues were for preaching as a sign to unbelievers in Israel, and as taste of things to come. If you were not one of them, it was as if they were babbling. No different than the circumcised church at Corinth who were not strangers to the covenants of promise.
The tongues meant nothing to those that didn't understand in their own language with out interpreation. Such as if you showed up, and nobody had been baptized that spoke canuck, you wouldn't have any idea what he was preaching.
1 Corinthians 14
6 But now, brethren, if I come to you speaking with tongues, what shall I profit you unless I speak to you either by revelation, by knowledge, by prophesying, or by teaching?
You would be full of wine.
8 For if the trumpet makes an uncertain sound, who will prepare for battle? 9 So likewise you, unless you utter by the tongue words easy to understand, how will it be known what is spoken? For you will be speaking into the air.
13 Therefore let him who speaks in a tongue pray that he may interpret. 14 For if I pray in a tongue, my spirit prays, but my understanding is unfruitful
1 Corinthians 13
8 Love never fails. But whether there are prophecies, they will fail; whether there are tongues, they will cease; whether there is knowledge, it will vanish away. 9 For we know in part and we prophesy in part. 10 But when that which is perfect has come, then that which is in part will be done away
Paul summarizes all of this, in case somebody gets the wrong idea.
1 Corinthians 14:22
Therefore tongues are for a sign, not to those who believe but to unbelievers; but prophesying is not for unbelievers but for those who believe.