Why should a Christian speak in tongues?
I believe that in the twety first century God does not want Christians to be speaking in tongues. There are two possible meanings of your question. I will try to give a very brief answer to both. One possible interpretation is you may be asking why did God have some of the Christians in the first century speak in tongues? Another possibility is that you may be asking why does God want Christians today to speak in tongues.
Let me answer the first question. The reason God had the Christians in the first century speak in tongues was to give approval to the message. They did not have the New Testament. Instead, the very early church had inspired teachers and inspired messages which were testified to by the miracles which were associated with them–including the speaking in various actual languages which the speaker did not know. I could give a rather long defense of this view, but let me just use a couple of passages. Hebrews 2:2-4 tells us that the New Testament message was confirmed by various signs, wonders, miracles and gifts of the Holy Spirit. This may not have been the only reason for speaking in tongues, but it certainly was one reason. I believe it was the main reason. Paul tells us that the gifts were given for the edification of the body (1 Corinthians 12:7-11). He also says that tongues (ie languages) were a sign to the unbelievers, not to believers. (1 Corinthians 14:22). I believe this is consistent with the idea that they confirmed the inspiration of the message.
What about the second question. What does God see as the purpose for speaking in other languages today? I am well aware that many will not agree with me on this, but I believe that God does not use the gift of miraculous tongues today. I believe this for a few reasons, and you should check what I say against the Bible and decide for yourself. First of all, the biblical evidence is that the miraculous gifts were passed along by the laying on of hands of the apostles. There is a lot of evidence for this claim. For example, consider Acts 8. Here Phillip has the miraculous gifts. He converts many to Jesus but he was not able to pass on the miraculous gifts. For this reason, he asked the apostles to come to Samaria to pass on the miraculous spiritual gifts. I will admit that I cannot absolutely prove that no one ever got these miraculous gifts by any means other than the laying on of hands, but I believe a very strong case can be made for this. Of course, the miraculous pouring out of the Spirit in Acts 2 and Acts 10, which was prophesied, is an exception. Second, the reason for the miraculous gifts, which was to testify to the inspired message, has passed. We now have the complete New Testament. The reason mentioned in Hebrews 2:2-4 has passed. So the means of giving the miraculous gifts has passed, as we no longer have living apostles and the reason has also passed. Further evidence is that church history tells us that by the second century the miraculous gifts had virtually completely disappeared. The only one even mentioned in the second century by the mainstream church is the gift of prophecy. Lastly, I have heard a lot about supposed speaking in tongues in a modern context. The best I can tell, this is not speaking in actual languages. I do not want to be disrespectful to people I believe are very sincere believers, but I believe they are speaking nonsense syllables. They are NOT speaking in actual languages as happened in the first century.
A lot more can be said on this, but I will leave it to you to look at the scripture and decide if what I am saying is true. I believe the correct answer is that God does not intend for you to speak in tongues.
John Oakes, PhD