The visible form that the Spirit took on Pentecost was that of fire. I'd like to share a few texts from the Byzantine Office for the feast. Fire and light (which is a property of fire) along with the gifts of tongues for preaching to the nations are the major themes.
"The Holy Spirit proceeds from the Unbegotten Light: the imperishable Resplendence who shines as a thousand lights, whose flaming word revealed...the consubstantial splendor inherited from the Father through the Son." Here we have all three images: the light, the fire, and the word that goes out to all the world. The manifestations of God are not for mere display or to prove that He is almighty. They are always "for our salvation," as we often pray in our Offices. They are for bringing people to the knowledge of the truth and to the way of life that leads to eternal blessedness in heaven. "The Lord has made eloquent the unlearned men of the sea, who by their words confounded the wise ones in their errors; and they brought countless people out of the deepest night, by the illumination of the Spirit."
The light and the fire of the Spirit are for us as well. We don't merely admire or celebrate something that happened 2000 years ago. The Fire of the Spirit is sent to purify us of sin and to ignite our cold hearts with the love of God: "the burning fire of the Spirit purifies our hearts and spirits from defilement." The Spirit will then give us "tongues of fire" to speak the truth with love to all those who need to hear the word of the Lord: "the Holy Spirit descends upon the apostles this day, and shining with the brightness of this fire, they make the Trinity known to all."
The Holy Spirit is not just brought out and dusted off for the feast of Pentecost once a year, and then returned to some dark closet of our consciousness till the feast rolls around again. The Spirit of God is our life. The Holy Spirit is intimately connected with the Holy Eucharist, so the "communion in the Holy Spirit"--listed by our Liturgy as one of the chief fruits of the Eucharist--is also our daily bread. After the consecration (during which we entreat the Father over the gifts of bread and wine: "change them by your Holy Spirit") we pray "that our loving God, who has received [the consecrated Gifts] as a spiritual fragrance upon his holy, heavenly, and mystical altar, may send down on us in return his divine grace and the gift of the Holy Spirit." Finally, after Communion we sing: "We have seen the true light and received the heavenly Spirit, we have found the true faith, worshiping the Undivided Trinity for having saved us."
Every day can be a little Pentecost. We ought to accept the Fire of purification, open our hearts to the Fire of divine love, and welcome the enlightenment so generously offered to all denizens of the darkness of the present age. Then go forth with tongues of fire and, like the heavens, speak of the glory of God (see Psalm 18/19).