May 15, 2016 is Pentecost Sunday. The church was established on the Jewish Day of Pentecost following the Resurrection of Jesus the Christ our Lord. He had ascended to Heaven a few days before (AD 32) and Peter and other Apostles gathered about 120 followers of Jesus together in a room for worship and meditation.
"When the day of Pentecost came, they were all together in one place. Suddenly a sound like the blowing of a violent wind came from heaven and filled the whole house where they were sitting. They saw what seemed to be tongues of fire that separated and came to rest on each of them. All of them were filled with the Holy Spirit and began to speak in other tongues as the Spirit enabled them." --Acts 2:1-4 (NIV)
Over several thousands of people began to gather to hear what was going on. They were from many other nations who spoke many different languages. They heard God's message in their own native tongue. They were amazed concerning this miracle. The Apostle Peter preached a terrific sermon and over 3000 were added to the church that day. This was the beginning of the Gospel being spread all around the world.
"Go therefore and make disciples of all the nations, baptizing them in the name of the Father and the Son and the Holy Spirit …" -- Matthew 28:19 (NASB)