John answered them, "I baptize in water, but among you stands one whom you don't know.
Such a comment misses the point.  John was answering the question of why he was baptizing; but, if Hendriksen's comment is what John meant, he did not answer the question at all.  The thought that "Well, my baptism is only a sign" is no reason at all for baptizing, but is rather a good reason for not baptizing!  It will be noted that there is no reference to the Holy Spirit in this passage.