What does it mean? What is the significance? How do we know for sure?
Originally Pentecost was a Jewish religious holiday going back to the feast of Weeks. However, in the New Testament it takes on a whole new meaning. In the New Testament it is referring to the outpouring of the Spirit of God (the Holy Spirit) which occurred shortly after Jesus ascended into Heaven after the Resurrection. It began with approximately 120 believers assembled together in the upper room waiting, just like Jesus told them to do. Suddenly there was a sound from Heaven that sounded like a mighty wind and each of the believers in the upper room were filled with the Holy Spirit. Cloven tongues of fire were seen on their heads and each of them began to speak in a tongue that was unknown to them. They were worshipping and praising God. The book of Acts contains the story.
Today many give Pentecost a place historically as though it was an occurrence limited to the days of the Apostles immediately following the ascension of Jesus. Certainly it is historically of vast importance but was it limited to the beginning of the Church age? What about today? There are many opinions but to know for sure we must examine the Word of God itself for the answer. Ac 2:39 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. Also look at Acts 2:33, 38. This scripture tells us that it is an ongoing event for the Church beginning at the say of Pentecost over 2000 years ago and extending to today.
Why? The outpouring of the Holy Spirit was to empower the Church to deal with the problems that confront it in such a way as to render to God the glory. It was and is an empowerment to overcome the devil whom Jesus defeated at Calvary. Acts 1:8 tells us that each one that received the infilling of the Holy Spirit (Holy Ghost) would receive power. Sometimes that power comes through the gifts of the Spirit as recorded in I Cor. 12. Other times it may be to simply resist the devil and he will flee from you. (James 4:7)
The book of Acts speaks of tongues as the initial evidence of having received the baptism of the Holy Spirit. What is that? Sometimes it is a foreign language (a language not known by the speaker). Other times it is a Heavenly or divine language wherein you are speaking directly to God and no one knows what you are saying, even the speaker. Why is this important? First it is submitting to God and overcoming the flesh and the mind. It is a spiritual thing. Secondly, the devil has no idea what is being said and therefore he has no idea of how to stop what is being said. How frustrating it must be for the devil. Speaking in tongues is not a physical thing but a spiritual. It is your spirit speaking from the innermost part of your belly. It is like a river gushing forth (Joh 7:38 He that believeth on me, as the scripture hath said, out of his belly shall flow rivers of living water.)
1Co 14:2 tell us “He that speaketh in an unknown tongue speaketh not unto men, but unto God: for no man understandeth him; howbeit in the spirit he speaketh mysteries.” You can see why it is not a mental process or a religious exercise but something involving only the speaker and the Holy Spirit of God. There is no scripture that says tongues were only for the days of the Apostles. It was given to empower the Church and certainly the church today needs an endowment with power from on high.