Matthew (The Book, Not My Son...)

We are reading through the NT this year.  The whole class.  I wasn't sure I was going to be crazy about that, but it's already been very enlightening and we're only 5 chapters in.  It's amazing how you pick up on new things in passages you've read 1,000 times.  Like Matthew 3, for instance. 

⁴ John’s clothes were made of camel’s hair, and he had a leather belt around his waist. His food was locusts and wild honey. ⁵ People went out to him from Jerusalem and all Judea and the whole region of the Jordan. ⁶ Confessing their sins, they were baptized by him in the Jordan River.


Wait a minute.  John was baptizing them.... Why was John baptizing them?  As far as I know, this is the first time baptism is mentioned.  God didn't command John to baptize.  And it's very odd that people would come to confess their sins and be baptized.  Why would they do this?  All this time I've been looking back on that with my NT Christian eyes - "Why they're getting baptized for the remission of their sins!"  But the act of baptism did not hold the same symbolism or significance.  I was very confused.  God didn't institute baptism?  This was a man-made act?  Where did the act originate from?  A very wise African man in class tried to explain it to me.  I tried really hard to understand.  But I'm still not sure I do.  And if a sect of Jews practiced baptism prior to the records we have in the NT, why did God choose to use that act as a means of salvation? I suppose that answer is for the symbolism, but I guess I mean, it seems like baptism popped up out of nowhere?  Am I missing something from the Old Testament?  This is really bothering me already....

I'm sure this is going to happen a lot.