Verse 1
Matthew 3:1 --
In those days -- Matthew intended his narrative to embrace the whole time of Jesus’ life, and the meaning of “in those days" references while Jesus still dwelt at Nazareth.
John the Baptist -- Or John the baptizer, so called from his call for people to repent and be baptized. Baptism was the immersion of candidates upon their submission to his message.
John the Baptist came preaching -- It is not probable that John began to baptize or preach long before the Saviour entered on his ministry; and, consequently, from the time that is mentioned in the close of the second chapter to that mentioned in the beginning of the third, an interval of twenty-five years or more elapsed.
preaching ... Mark 1:14-15; The word rendered “preach” means to proclaim in the manner of a public crier; to make proclamation. The discourses recorded in the New Testament are mostly brief, sometimes consisting only of a single sentence, but they may have just been an outline, or an abbreviation of the full message. They were public proclamations of some great truth. Such appear to have been the discourses of John, calling people to repentance.
in the wilderness of Judea -- This country was situated along the Jordan and the Dead Sea, to the east of Jerusalem. It was a dry mountainous, rough, and thinly settled country, and better suited for pasture than for tilling.