Rather than begin his work by going to any of these powerful people or the people around them, John, like Moses and like Isaiah, whose words he quotes, goes into the wilderness to speak.
John calls for a baptism of repentance. Isaiah, in speaking out against the wickedness of Judah, had called upon them to "Wash yourselves; make yourselves clean; remove the evil of your doings from before my eyes; cease to do evil, learn to do good; seek justice, rescue the oppressed, defend the orphan, plead for the widow" (1:16-17).
Jerusalem in John's time would have had evil, injustice, oppression, and many people who needed financial help. He was calling his listeners to repent--to change their ways.
John also specifically includes Isaiah's prophecy that all people are included in the promise of salvation (Luke 3:6; Isaiah 40:5).