Based on this passage: And there appeared to them parted tongues as it were of fire, and it sat upon every one of them: And they were all filled with the Holy Spirit, and they began to speak with divers tongues, according as the Holy Spirit gave them to speak” (Acts 2:2).
K. Van de Vyvere, Brugge, Belgium
"Then He came to the creation of man, and He created one man; and from one man the human race. Nor did He will to create two separate beings, male and female, but one man; and from this one man He made woman (Gen. i. II). Why did He do this? Why did He begin the human race from one man, if not to commend unity to mankind? And the Lord Christ was born of one person. In the Virgin therefore is unity..." from Homily for the Day of Pentecost: St. Augustine
Other links:
St. Cyril of Jerusalem's sermon ~ The Holy SpiritMakes Himself Known by His Fragarance from Enlarging the Heart
Sermon on the Feast of Pentecost ~ from The Saint Gregory Palamas Outreach