“Was John’s baptism a new ordinance or were the people already familiar with it?” Ensign, Sept. 1974, 16
Dr. Robert J. Matthews, associate professor of ancient scripture, Brigham Young University: Baptism by water was not new to the Jews of New Testament times. Although it is not completely clear from either secular history or the scriptures that the Jews were actually baptizing one another at that time, it was a regular practice among them to baptize gentile converts to Judaism. (See Madeline S. and J. Lane Miller, Harper’s Bible Dictionary, New York, Harper and Row, 1961, p. 60, “Baptism.”) Baptism was known to Adam and the patriarchs (see Moses 6:53–59; Moses 6:65; Moses 8:24), and it was an integral duty of the Aaronic Priesthood under the law of Moses (see D&C 84:25–28; 1 Cor. 10:1–4). Also, the Dead Sea groups seem to have been practicing washing and immersion in water as a religious performance. Therefore, baptism was known to the Jews in the meridian of time.
It is noticeable that when John came among the people, they did not ask him, “What new thing is this that you do?” but rather they asked, “Who are you?” They did not question the ordinance, but they did want to identify John. For this purpose a delegation from the Pharisees was sent to question him. They pointedly inquired if he were the Christ, or if he were Elias. (See John 1:19–21.) These questions were the result of their own conclusions about the scriptures. It is evident that they had anticipated the coming of a Messiah and/or an Elias who would perform baptisms. Therefore, when John came among them baptizing, they wondered if he might be one of those persons. When he denied that he was the Christ or the particular Elias to whom they had reference (one who would restore all things rather than one to prepare a way), they asked him again: “… Who art thou? that we may give an answer to them that sent us. What sayest thou of thyself?” (John 1:22.) They also asked him, “… Why baptizest thou then, if thou be not that Christ, nor Elias, neither that prophet?” (John 1:25.)
That such a discussion took place between the Jewish rulers and John the Baptist indicates they were familiar with the ordinance of baptism.