Pentecost was the second of the three major feast days for the Jews.  Its name comes from the fact that it was celebrated fifty days after the Passover.  The Passover was when the children of Israel made their exodus from Egypt and then 50 days later the law (The Ten Commandments) was given to Moses.  It is no coincidence that Jesus was crucified during the Passover and then the outpouring of the Holy Ghost took place on the day of Pentecost.  Jesus became the spotless lamb that brought our exodus from sin and then his spirit was poured out upon the church at the beginning of the book of Acts, signifying God’s command.  We believe that the experience that took place on the day of Pentecost was not just for that time it was an experience that you and I can and should have today. 

Acts 2:37-39
37 Now when they heard this, they were pricked in their heart, and said unto Peter and to the rest of the apostles, Men and brethren, what shall we do?

38 Then Peter said unto them, Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost.

39 For the promise is unto you, and to your children, and to all that are afar off, even as many as the Lord our God shall call.
KJV

What were key elements of this day?

• Jesus told them to tarry until they were endued with power from on high
• The Holy Ghost was promised to give them power to do great things
• The evidence of the Holy Ghost was that they spoke with tongues as God spoke through them.

Acts 2:4

4 And they were all filled with the Holy Ghost, and began to speak with other tongues, as the Spirit gave them utterance.
KJV