Pentecost is also called the "birthday" of the Church because it is the beginning of the preaching ministry of the disciples. Pentecost celebrates the sending of the Holy Spirit into the world, which is the Spirit of unit, the Spirit of love, the Spirit of truth, the Spirit of wisdom. This the same Holy Spirit that was given to us at our baptism and chrismation (or confirmation as they say in the Western Churches), the same Holy Spirit given to clergy at their ordination, and the same Holy Spirit that comes upon us at every Divine Liturgy or Mass.
I wish everyone a good Pentecost season. I hope that you realize that the Holy Spirit is alive and active in the world, in the Church, and in your life. Each one of us received the gift of the Holy Spirit at our baptism, don't forget that.
If you want to read more about Pentecost from an Eastern Orthodox perspective and other feast days click here