“καὶ ἐβαπτίζοντο ἐν τῷ Ἰορδάνῃ ποταμῷ ὑπʼ αὐτοῦ
ἐξομολογούμενοι τὰς ἁμαρτίας αὐτῶν ”
http://ref.ly/r/ldgnt/BibleNA27.Mt3.6 via the Logos Bible Android app.
Faithlife Study Bible notation:
3:6 they were being baptized Likely derived from the Jewish custom of ritual washings. These baptisms were intended to signify spiritually cleansing in preparation for the coming of the Messiah.
Jordan River The Jordan was significant for the Jewish people of the time because it served as the border Israel crossed into the promised land. It does not seem to have been important for ritual washings, except in the case of Naaman the Syrian (2 Kgs 5:10, 12).