When the Most High came down and confused the tongues in Babel, he divided the nations. But when he distributed the tongues of fire, he called all to unity. Therefore, with one voice, we glorify the Holy Spirit!
The Holy Spirit that Christ had promised to his disciples came on the day of Pentecost (Jn 14:26, 15:26; Lk 24:49; Acts 1:5). The apostles received "the power from on high," and they began to preach and bear witness to Jesus as the risen Christ, the King and the Lord. This moment has traditionally been called the birthday of the Church.
When the day of Pentecost had come they were all together in one place. And suddenly a sound came from heaven like the rush of a mighty wind, and it filled all the house where they were sitting. And there appeared to them tongues as of fire, distributed as resting upon each one of them. And they were all filled with the Holy Spirit ... (Acts 2:1-4).