The feast of weeks or grain festival is celebrated by those of the Jewish faith to commemorate the giving of the Torah on Mt. Sinai 50 days after the second night of Passover following Israelite exodus from bondage in Egypt. In Hebrew this celebration is called Shavuot and means “weeks”. In ancient Greek the word is Pentecost.
It was on the day of Pentecost after Jesus’ resurrection that the Holy Spirit descended upon the apostles whom were gathered together:
And when the day of Pentecost was fully come, they were all with one accord in one place. 2 And suddenly there came a sound from heaven as of a rushing mighty wind, and it filled all the house where they were sitting. 3 And there appeared unto them cloven tongues like as of fire, and it sat upon each of them. 4 And they were all filled with the Holy Ghost, and began to speak with other tongues, as the Spirit gave them utterance. AV
For the crowds gathered in Jerusalem:
5 And there were dwelling at Jerusalem Jews, devout men, out of every nation under heaven. 6 Now when this was noised abroad, the multitude came together, and were confounded, because that every man heard them speak in his own language. 7 And they were all amazed and marvelled, saying one to another, Behold, are not all these which speak Galilæans? 8 And how hear we every man in our own tongue, wherein we were born? AV
This miracle by the Lord got the attention of the crowd and Peter and the apostles gave witness of the Lord Jesus Christ and nearly three thousand were saved that day. This day has traditionally been the sermon that began the church and ushered in the church age that we still live in. When tongues are referenced it is a language and is not some incomprehensible sound. God in that day used another miracle to witness and convince people. Today and every day you can experience that witness by reading and studying the complete record from God to teach and inspire you and witness to all you meet – The Holy Bible!