When did things change?

Here's something that I have always wondered and quite frankly I don't know the answer. 

Mark 7:5-8(NKJV)

5Then the Pharisees and scribes asked Him, “Why do Your disciples not walk according to the tradition of the elders, but eat bread with unwashed hands?”

6He answered and said to them, “Well did Isaiah prophesy of you hypocrites, as it is written:      ‘This people honors Me with their lips,     But their heart is far from Me.

7    And in vain they worship Me,      Teaching as doctrines the commandments of men.’ £

8For laying aside the commandment of God, you hold the tradition of men—£the washing of pitchers and cups, and many other such things you do.”

Mark 7:14-16(NKJV)

14When He had called all the multitude to Himself, He said to them, “Hear Me, everyone, and understand: 

15There is nothing that enters a man from outside which can defile him; but the things which come out of him, those are the things that defile a man. 

16If£ anyone has ears to hear, let him hear!”

What I've always wondered is who decides what is  a "commandment of man" and what isn't?  There are many things that are in the Bible that are no longer done.  Were those commandments of man and if so then what were they doing in the Bible?  If not then why don't we still do them?

If you look at the second highlighted part you see Jesus saying " There is nothing that enters a man from outside which can defile him; but the things which come out of him, those are the things that defile a man."

OK.  That goes back the whole what's in your heart issue so that makes sense and I get that.  But at the same time you had God in the OT telling the people that they couldn't eat pork and shellfish, etc.  Now you have Jesus say "Aw that doesn't matter".  So which is it?  Was God mistaken?  Did He change His mind? 

Here are a couple of other examples.  Back in the old days King David and King Solomon had multiple wives as well as concubines.   Now I have a great wife and I'm not looking for another one or anything but when did that change?  I can't find where in the Bible God all of a sudden said don't do that anymore.

In the OT the Jews were told to offer all of these different sacrifices of animals at different times and for different reasons.  Today the Jews still  celebrate the different festivals but I'm not aware of animals being sacrificed.  When did God say to stop that?

As I said above, I don't have an answer, only the question.  I think it is important that believers realize that it is normal and OK to have questions even after we are saved.  God gave us an intellect and I think He expects us to use it.  At the same time God is way smarter than we are so I don't think He is threatened by our questions. 

So how do I deal with an issue like this?  Ultimately it’s not that big of deal to me.  It is something I ponder at times but I am confident that if it is something that I really need to know the answer to here on earth then God will see that I receive that revelation when I need it.  If not then it just goes on my list of things to ask God when I get to Heaven!