pentecostals believe the Hols Spirit will come into your heart and give you the Holy Gift of speaking in tounges.
based on the Pentecost. where the 11 disciples spoke in tounges, with licks of fire on their heads, witnessing to 1000s in one day.
today, they believe you are not full of the Holy Spirit unless you recieve the Gift. once you do, you are truly in God's hands, with His Spirit giuding you, and blessing you.
funny thing about speaking in tounges, in the Bible it speaks about it being a waste of a Gift, showing off if you will, unless there is someone with the Gift of translating it. i do not know the exact passage, or wording, but im sure if you know how to use a concordance you can find it. i believe it is in one of Paul's letters.
hawklore... are you / your family pentecostal?