"When the Most High descended and confused tongues, he scattered the peoples, but when he divided the tongues of fire, he called all to unity. Therefore, with one voice, let us praise the Most Holy Spirit." - Kontakion for Pentecost (Tone 8), Byzantine Rite
The coming of the Holy Spirit heals the divisions of the Tower of Babel, not by returning all of humanity to the use of one language, but by empowering the Apostles (and their successors) to proclaim one gospel, one message of good news for all people everywhere and for all time, regardless of the language they speak. This is the first and primary meaning and purpose of the "gift of tongues". Ecstatic prayer, while possible, is secondary.
Fr. Hosea has a Pentecost homily by Metropolitan John of Pergamum, formerly known as John Zizioulas, the author of Being as Communion.
"Come Holy Spirit! Sanctify our Lives!"