There are three laws given in this text: The law regarding the cities of refuge. The law regarding boundary markers. The law regarding witnesses. These three are connected.
Cain was the first man to kill another man and men continued to kill men until God destroyed the earth with a worldwide flood. During the time of Noah, God commanded:
Whoever sheds man’s blood,By man his blood shall be shed,For in the image of GodHe made man. (Genesis 9:6)
Human life is superior to that of the animals because we were created in the image of God. Murder is defined as malice of forethought. It is an intended act. In our society, some may disagree with the concept of life for life, eye for eye, tooth for tooth, hand for hand, foot for foot justice until it happens to them or someone that they love. When it does, they want vengeance.
The law regarding the cities of refuge were put in place to protect the innocent. We live in a dangerous world, were accidents happen and people lose life and limb. So, intention of the heart and mind is the determining factor. We do not take it upon ourselves to avenge blood, this power is given to the state. In the nation of Israel, it was given to the elders, because anger is never just. Witnesses plural were required to convict a person of wrong doing. A single person might attempt to use the elders to do harm to his neighbor, whom he hates. Multiple witnesses are required to lesson the probability of false judgments.