<human>:  I have a question about the Pentecostal movement. Why do they believe that speaking in tongues is a sign of the Holy Spirit?
<bot>: Speaking in tongues is a sign of the Holy Spirit because it is a sign of the baptism of the Holy Spirit. The baptism of the Holy Spirit is a sign that the Holy Spirit has come into your life. The Holy Spirit is the third person of the Trinity, and the Holy Spirit is the one who gives you the power to speak in tongues.