Deuteronomy 16-19

I am finding it so refreshing to read about some of the things we've already read about with a little more understanding (if that makes any sense).  I don't know that I fully understood the reasoning for some of the things the people of Israel have been asked to do.  For example, the eating of the unleavned bread, or the bread of affliction, was required because the Israelites left Egypt "in haste."  This is supposed to remind them every day of their departure from Egypt.  Also, the Passover is to occur on the anniversary of their departure from Egypt in the place that the Lord chooses, and no where else.
We then learn about the Feast of Weeks and how the people are to give a freewill offering to God "in proportion" to the blessings the Lord has given them.  Can you imagine??  I know I would have to give quite an offering!
When reading about the decree of worshipping other gods, it was interesting to see that anyone found guilty would be stoned to death.  However, you would have to have more than one witness.  If only one person said this was true of another, their testimony didn't necessarily count.  Also, once the Israelites enter the promised land, they will be blessed with another prophet, just like Moses.  The Lord will send his commands through this prophet, and the people will know who he is because everything he tells will come true.  If it doesn't, they will know he is an imposter. 
Finally, I have a bit more understanding in the cities of refuge that are to be built.  Once the Israelites are settled, they are to build 3 cities outside of their own.  This is where people are to go to save their own lives.  If they accidentally kill someone, they are to flee to one of these cities to be "safe."  If they do not, they will be killed.  If a person killed someone intentionally and they flee to one of these cities, they will be brought back and put to death.  I don't quite understand the reasoning behind this.  Why can't there just be an accidental death and have everyone still live in the same town?  There is obviously a good reason for it, but one I still haven't figured out. 
Once again, I am really enjoying Deuteronomy!