... continued from Wednesday.
"When the day of Pentecost came, they were all together in one place" (Acts 2:1). There were about 120 in an upstairs room (1:15), quite possibly the room where they ate the Last Supper (Luke 22:12).  The number included the original eleven disciples, others who had followed Jesus from the beginning (like Matthias and Joseph), and women who had followed Jesus (cf. Luke 23:55-56). It also included Jesus' mother, Mary, and Jesus' brothers like James and Jude. They have been praying and waiting on the Holy Spirit to come, as Jesus promised.
They hear a violent wind. The word for spirit in both Greek and Hebrew is related to the word for wind. The Spirit is, in a sense, the breath of God, breathing on his people, giving them life as in Genesis 2:7. The tongues of fire are like traditions about what happened when God gave the Law on Mt. Sinai, except now God is enacting the new covenant, in which he writes his laws on the hearts of his people through the Holy Spirit. 
They begin to speak in other languages or "tongues" as they are often called. They apparently come out of the upper room to the outside and are telling of the wonders of God in all sorts of different languages. It is the Feast of Pentecost. Jews are in Jerusalem from all over the known world. Fifteen different areas are mentioned. Parthians, Medes, Elamites, and people from Mesopotamia hear, people from the far east of that time. Cappadocia, Pontus, Asia, Phrygia, and Pamphylia are places in modern day Turkey. Egypt and Libya are in Africa, Crete and Rome from the broader Mediterranean. Arabs lived in Palestine and Judea was of course where Jerusalem itself was.
These are Jews and converts to Judaism. We remember that there were more Jews scattered outside of Jerusalem at the time than lived in the home country. The Egyptian city of Alexandria alone probably had more Jews in it than in all of Jerusalem. These individuals hear the witness of the 120 in their own languages.
Probably the most natural way to take the tongues of Acts 2 is that these individuals are given the ability to speak in these other languages. The only hint of something different would be the fact that some think that they are drunk. The situation in Acts 2 points to something a little different from 1 Corinthians 14:23, when outsiders do not understand what is being said. The tongues-speakers in 1 Corinthians 14:13 also do not seem to know what they are saying, while those in Acts 2 presumably do. The experience in Acts 2 is a tool for witness and mission. In 1 Corinthians 14 it is a very personal experience that Paul criticizes for not being edifying to the congregation as a whole.
Tongues come in two other places in Acts. In Acts 10:46, Gentiles speak in tongues when the Spirit first comes on them. This is the first time in Acts that the Spirit comes on the Gentiles, proving that they can be in the people of God without having to convert to Judaism and get circumcised. Speaking in tongues shows that their experience of the Spirit is every bit as authentic as the Spirit-filling experience the Jews experienced on the Day of Pentecost.
But tongues are not mentioned every time someone is filled with the Spirit. For example, tongues are not mentioned in another filling the followers of Jesus experience in Acts 4:31. Tongues are not mentioned at Samaria when the Spirit comes (8:17) or when Paul receives the Spirit in 9:17-18. The only other place tongues are mentioned is in Acts 19:6 at Ephesus.
The situation here is that some individuals have only been baptized in the way of John the Baptist. They have not been baptized in the manner of Jesus, which involves receiving the Holy Spirit. So Paul baptizes them and the Holy Spirit comes on them. They speak in tongues just as the disciples had on the Day of Pentecost.
Tongues in these instances seem to be particularly significant as a sign of the new age of the Spirit. In each instance, some important boundary is crossed or is remembered being crossed. There are some groups that insist that anyone who is truly a Christian will speak in tongues. Such groups often put Acts 2 at the center of their understanding of Christian life today. There are at least two key features of their understanding.
The first is that receiving or being filled with the Holy Spirit is part of a person's conversion experience. We will look at this issue in a moment. Are the Spirit-fillings of Acts an initial experience that believers have when they first come to believe on Jesus as their Lord? Or is receiving the Holy Spirit a second or later experience a person has some time after he or she has believed? For that matter, do all Christians receive the Holy Spirit at all or is it a special experience just for some?
The second assumption is that all those who receive the Holy Spirit in Acts spoke in tongues, even though Acts does not always mention them. Certain Pentecostal groups distinguish between tongues in Acts as the key evidence that a person has received the Holy Spirit and tongues as a special gift from God that only some Christians receive. Such groups would say that 1 Corinthians 14 is about the gift of tongues, while Acts 2 tells us about tongues as evidence that a person has in fact truly become a Christian.
There are good reasons to believe that not all Christians will speak in tongues when they first believe...
 Was it the home of John Mark in Acts 12:12?
 Cf. Jer. 31:31-34; Heb. 8:8-12; Rom. 2:15.