I'm going to make every effort here to be non-denominational in my study of the following scripture.  However, as you well know, I am a Reformed Presbyterian (PCA), and so my own beliefs may filter through. 

2As it is written in Isaiah the prophet,

   "Behold, I send my messenger before your face,
 who will prepare your way,

3the voice of one crying in the wilderness:
   'Prepare the way of the Lord,
   make his paths straight,'"

Before we go much further, I’d like to stop here for a moment.  Mark has chosen to do something very interesting here.  While much of Mark, as we have said, is a very kinetic book – it focuses a lot on the actions of Jesus, Mark does take the time to make a connection with his readers and the history of Jesus Christ.  Most Christians at the time of the writing of Mark would have come from Judea / Israel, and would have either been Jewish or would have made some connection with Jewish scriptures, since the New Testament had not yet been written – and wouldn’t be completed for another 40 years or so.  In other words: the Old Testament WAS the Bible as far as Mark would have been concerned.

Mark’s first action after introducing his purpose in writing this Gospel is to make a connection with 2 prophets: Malachi and Isaiah, which gives us a good idea of exactly who the prophets of Israel were looking for.  While the rest of Israel was looking for a literal king or rebel leader to free them from Roman oppression, Malachi was looking for someone different.  In fact, looking at the entire verse in Malachi, we see that the messenger was preparing the way for someone who would “suddenly come to his temple”.  We’ll see more of this later on in Mark. 

And, yes.  I'm well aware that the verse above says "Isaiah".  There are lots of theories as to why this verse includes "Isaiah" when the verses come from Malachi, and to a lesser extent, Deuteronomy.  My favorite is the concept that a well-meaning copyist included it because he knew recognized the part that came from Isaiah, but the fact is: we just don't know.  "Isaiah" appears in some older manuscripts and doesn't appear in others.  My opinion is that Mark would have been well-aware that his readers were just as picky as the pickiest theologian today, and would have known what parts of this verse came from what books, and would've called him on it.

So what we actually have here is Mark beginning to make the case – he’s beginning to lay out the evidence for the case that is Jesus as the Messiah – as the Christ.  He’s reaching back to Isaiah and Malachi (both of whom early Christians would have been familiar with) to prepare his case.  He’s laying the foundation.  Now, let’s see how that foundation is getting built:

   4John appeared, baptizing in the wilderness and proclaiming a baptism of repentance for the forgiveness of sins. 5And all the country of Judea and all Jerusalem were going out to him and were being baptized by him in the river Jordan, confessing their sins. 6Now John was clothed with camel's hair and wore a leather belt around his waist and ate locusts and wild honey. 7And he preached, saying, "After me comes he who is mightier than I, the strap of whose sandals I am not worthy to stoop down and untie. 8I have baptized you with water, but he will baptize you with the Holy Spirit."

Here, we have the very beginning of New Testament action.  John the Baptist (or Baptizer, if you’d prefer) is starting to preach what will become a basic Christian doctrine, and one of two elements that all Christians consider to be a sacrament: baptism.  Now, there are different theories on the theology and doctrine of baptism that we won’t get into just yet (ranging from dunking vs. sprinkling, paedeobaptism vs. credobaptism, etc.), but the point is this: John started the foundation.  He preached a need for repentance of sins, which apparently was hitting people exactly where they lived: “And all the country of Judea and all Jerusalem were going out to him and were being baptized by him in the river Jordan, confessing their sins.”  He was preaching something that these people recognized and knew that they needed (it wasn’t because he was a popular, clean-cut, nice-looking guy, what with his camel hair outfit and diet of bugs and honey….).  They knew:

A.  That there was a law set down by God; and
B.  They weren’t following it.

See – John wasn’t really asking Jews just to get wet.  Baptism was a real thing in the Jewish faith, and it was taken very, very seriously.  While groups like the Essenes baptized themselves daily for purification, most Jews were only baptized upon conversion to Judaism.  What John was asking these Jews to do was to lower themselves, humble themselves, to the level of a new convert.  He was calling on them to acknowledge that their ability to follow the law hadn’t changed their hearts, and that they were still in need of repentance and of God’s grace – and his listeners responded by coming in droves.  Thousands of proud, religious Jews going to be humiliated in front of each other, living, breathing examples of how the law’s training wheels weren’t producing the grace that these people needed.

Now, there are a couple of other things that I’d like to point out...

1.  John’s Appearance is actually important.  While he was kinda strange walking around in his camel hair and leather belt, John was actually making a reference back to the Old Testament.  Back in II Kings, there was a famous prophet who was walking around in camel hair and a leather belt – and nobody recognized him - Elijah.  In Malachi, God promised that He would send Elijah before the Day of the Lord.  Now, while John the Baptist wasn’t the actual physical Elijah, He was exactly what God promised.  He was a prophet who believed that Jehovah was his God (which is what “Elijah” means).  He was indeed the prophet before the Day of the Lord.  John's appearance was another chunk of evidence that the prophecy of the Christ was about to be fulfilled.

2.  Baptism – now’s a good time to address baptism.  There are a lot of issues that come in with Baptism, and it’s not going to be easy (or quick) to cover them all.  I’m going to give you the basics here, and if you’d like my opinion on the matter, we can discuss it in the forums.  Keep in mind: these are Cliff's Notes on the subject - there are many, many other books and scholarly writings that go into much better, much greater detail than I will here.

On methods:

a.  Full Immersion: the belief that the Greek terms “bapto” (temporary) and “baptizo” (implying permanence) mean to submerge completely in liquid.  This method has historical backing in the Eastern Churches, and has found its way into the modern Baptistic churches.  It is usually based in scriptures such as Mark 1 that show Jesus “coming up out of the water”.

b.  Pouring / Sprinkling: the belief that these terms also mean “pour” or “sprinkle”, and that baptism takes place upon the ceremonial sprinkling of water.  This method has historical backing in the Western Churches, and is commonly practiced by non-Baptistic churches.  Scriptures used in favor of this include Acts 8:36, and others that show that these terms may reflect multiple possible definitions.

On who may be baptized:

a.  Credobaptism: the belief that only confessing Christians should be baptized.  Based on repeated scriptures that say “believe and be baptized”.

b.  Paedobaptism: the belief that Baptism should be performed on "covenant children" - children of believers.  This is often called “infant baptism”, and is based on scriptures such as Acts 2:38-39 and Acts 16:31ff, among others.

On the salvific / effective nature of Baptism:

a.  Baptismal Regeneration: The belief that, under usual circumstances, a person is not fully a Christian until they have been baptized - or (sometimes) have expressed a desire to be baptized.  Based on repeated scriptures that indicate that acceptance of the Gospel and Baptism were connected.

b.  Baptism as a Sign and Seal of the New Covenant: the belief that a person is a member of the family of God upon conversion regardless of Baptism, and that Baptism is a sign and seal of the covenant between the believer and God.   Based on many scriptures where circumcision is replaced with Baptism in the NT.

c.  Baptism as an Outward Sign of Inward Change: the belief that Baptism is a reflection of the Holy Spirit's action on a person after that person has been saved.

Note: while there is a difference concerning efficacy among the various theologies, I am unaware of any Christian group that considers a refusal to be baptized as an acceptable behavior, and every group I am aware of would seriously question that person's salvation.

Back to Mark.  Back to John, the camel-hair-clad, bug-eating baptizer from the desert that was the fulfillment of the prophecies...

Now, if John thought he was the cat’s meow, he didn’t show it.  In fact, he actively denied it.  John himself said that Someone Else was coming coming whose sandals he not even worthy to touch, who’ll preach the same repentance, but instead of water, He’ll baptize you with something you’ve never even seen…

The sandals comment is very interesting, especially considering how Middle Eastern cultures tend to view shoes: badly.  Have you ever heard that showing the bottom of your shoe to someone from the Middle East is a grave, grave insult?  Have you ever heard about protests where Middle Easterners threw shoes at people?  Ever wonder why?  It's because shoes are...  well, they're dirty.  Sure, they kept your feet protected, but those shoes are just plain nasty...  they're just about the dirtiest form of clothing that a human can have, outside of toiletries, and to toss a shoe or show the sole of your foot to a Middle Easterner, such as an Arab or a 1st-Century Jew, is to basically say, "You are utterly beneath me."  And yet, John seems to have taken the concept of him being utterly beneath the coming Christ as a place of honor.