Somewhat relating to this question.
Many times I have been asked by members of some protestant denominations (especially by Baptists and Pentecostals) whether I've been baptized, followed by the question of whether I've been baptized by the Holy Spirit? After they ask me or others this question, they stress the utter neccessity of this kind of baptism.
This question is very confusing for many christians, leading them to doubts about their baptism.
Upon asking the enquirer about what they mean by "baptism by the Holy Spirit" they describe experiences of being filled with the Holy Spirit (yes, I've had such experiences). Some say that baptism by the Holy Spirit may happen before being formally baptized, some say it may happen after, but all stress the importance of it, as if without such an experience one had no hope of salvation. When I ask them whether each such experience constitutes a baptism, they usually get confused and answer that only the first of such experiences constitutes a baptism.
Why do they make such confusing distinctions and call these experiences baptism? Do they consider the traditional baptisms administered by priests (in the name of the Father, the Son and the Holy Spirit; with water and together with the laying on of hands and prayers for the Holy Spirit, etc) invalid or incomplete? Do they consider the traditional forms of christian baptism to be baptism by water only? What are the roots of this semantical error or false teaching? Where does it come from?