Pentecost is derived from the Greek word for fiftieth. It occurs fifty days after the sabbath of the week-long Feast of Unleavened Bread. People brought a free-will offering of their first grain to Jerusalem for Pentecost. Jerusalem offers God a kind of free-will offering on this Pentecost as three thousand people accept Jesus as their Savior.
Jesus instructed His followers to wait in Jerusalem for the Father's promise. For ten days, the followers of Christ waited in anticipation of being baptized with the Holy Spirit. The fact remains, however, that only 120 of Christ's followers were gathered in one place at that time. They were at the right place at the right time. This means that they were the ones who would receive the promise from the Father on that day. 
In the midst of these 120 faithful disciples answering Christ's call, it must have been an amazing day when the fledgling Church was born. On that day, they were baptized with the Holy Spirit, as Christ had promised ten days earlier. They also received the gift of tongues from the Holy Spirit, for we hear that they spoke in languages as the Spirit gave them utterance.

Dear Heavenly Father, it was a special and unique day of Pentecost when 120 disciples obeyed Your Word. They were blessed with the privilege of witnessing the birth of the true Body of Christ, which is the Church. Like them, I pray that I will listen to Your commands and carry them out willingly. In Your Church, may I devote myself to the teaching of Your Word and to fellowship with one another to Your praise and glory. 
In Jesus's name I pray. Amen.