See also Isaiah 40:3-4
I keep thinking there is something to the people that come to John for advice. One thing I can think of is that if publicans and soldiers are coming to him honestly seeking advice, then he was someone who people respected, out of many stations in life. All kinds of people are eager to hear God's word. In fact, it says that the publicans came to be baptized. It is easy for me to write off certain types of people (like rich lawyers or bullying officers) as not interested by their very nature, but we see here that is not the case.