James D.G. Dunn, Baptism in the Holy Spirit, p. 2, on the Pentecostal Tradition:
As a result of their own experience the early pioneers of this movement came to believe that the baptism of the Holy Spirit is a second (Pentecostal) experience distinct from and subsequent to conversion which gives power for witness (Acts 1.8), that speaking in tongues, as in Acts 2.4, is the necessary and inevitable evidence of the 'baptism', and that the spiritual gifts listed in 1 Cor. 12.8-10 may and should be manifested when Pentecostal Christians meet for worship. As so often happens in such cases, succeeding generations have hardened these early less rigid beliefs into dogmas of Pentecostal tradition.
This has been the source of my love-hate relationship with Pentecostalism over the years. I came into Christianity through Pentecostalism, but I haven't been a confessing Pentecostal in about a decade. Pentecostalism has inspired me when it invites us into a Christianity that isn't just doctrinaire, isn't just creedal, isn't just for the literate and educated. Pentecostals upsets me to no end when experiences like glossolalia because something you must experience rather than something you can feel free to pursue.