By the mouth of witnesses A wise precaution to prevent the shedding of innocent blood. If we may credit the Jews, where there was but one witness, and the person accused of murder could not, therefore, be put to death, yet he did not escape without punishment, but was thrown into a very strait prison, and there fed with bread and water. Ye shall take no satisfaction This rigid severity of the law served to impress the minds of the people with a deep sense of the heinousness of the crime of murder, since nothing less than the blood of the murderer could compensate for the crime, and cleanse the land from its pollution. And it is but just in itself that life should pay for life.
Related Commentaries of Numbers 35:30
Numbers 35:30-31
30 Whoso killeth any person, the murderer shall be put to death by the mouth of witnesses: but one witness shall not testify against any person to cause him to die.
31 Moreover ye shall take no satisfaction for the life of a murderer, which is guiltya of death: but he shall be surely put to death.