Where did John the Baptist get the idea to dunk people in water and call it baptism? It can't be the same as our baptism today, depicting the death, burial, and resurrection; that hadn't happened yet. He preached baptism for the remittance of sin. But where did the idea come from?
Thanks for your question. D.S. Dockery has a good discussion of this issue in his article on "Baptism" in the Dictionary of Jesus and the Gospels [eds. Joel Green and Scot McNight (Illinois: Intervarsity Press, 1992), 55-58].
Although the Jews practiced a form of proselyte baptism, "there is no clear evidence prior to A.D. 70 that proselytes underwent baptism as a requirement of conversion" (Ibid., 56). Dockery presents the following arguments against the view that Jewish proselyte baptism served as the model for John's baptism (ibid., 56):
But if John did not get this idea from Jewish proselyte baptism, where did he get it? Dockery thinks a more likely borrowing occurred from the Qumran community. He does not, however, commit John to having been an Essene. In support of his thesis, Dockery offers the following arguments (Ibid., 57):
However, there was one important distinction between the Qumran community and John regarding baptism: the Qumran rite was self-administered and practiced frequently, while John's baptism was administered by John and was a one-time rite of initiation.
Thus, Dockery believes John got his idea for water baptism from the Qumran community. Of course, it's important to note that if John originally received this idea from Qumran, he nonetheless revised and adapted it to fit his own unique purpose and calling as the one who was preparing the Jewish nation to receive her Messiah. Also, it's important to remember that this is simply one scholar's expert opinion. I happen to think it a good one, but as he himself observes, "...the background of John's baptism remains fiercely debated" (Ibid., 56).
God bless you,