Matthew 3:5

Then went out unto him Jerusalem, and all Judaea, and all the region round about Jordan; And they were baptized of him in the river Jordan, confessing their sins.

All Judaea ...; Matthew 3:5 is hyperbole in which there is an intentional exaggeration for the sake of emphasis. There are many figures of speech in the Holy Scriptures, and a proper understanding of them is necessary to a true understanding of God's word. There are other figures which shall be noted in this chapter. Matthew 3:5 merely means that the great majority of the people of that time and place accepted the baptism of John the Baptist. It is specifically declared in the Scriptures that the Pharisees and lawyers did not accept it (Luke 7:30).

In the river Jordan ... John selected this river as the scene of his many baptisms for a reason, and the reason is given in John 3:23, "because there was much water there." This makes it imperative that immersion be understood as the "form" of baptism practiced by John, since "much water" could not possibly have been required for any other "type" of baptism.