Deuteronomy 19:4

"And this is the case of the manslayer, that shall flee thither and live: whoso killeth his neighbor unawares, and hated him not in time past; as when a man goeth into the forest with his neighbor to hew wood, and his hand fetcheth a stroke with the axe to cut down the tree; and the head slippeth from the helve, and lighteth upon his neighbor, so that he dieth; he shall flee to one of these cities and live: lest the avenger of blood pursue the manslayer, while his heart is hot, and overtake him, because the way is long, and smite him mortally; whereas he was not worthy of death, inasmuch as he hated him not in time past. Wherefore I command thee, saying, Thou shalt set apart three cities for thee. And if Jehovah enlarge thy border, as he hath sworn unto thy fathers, and give thee all the land which he promised to give unto thy fathers; if thou shalt keep all this commandment to do it, which I command thee this day, to love Jehovah thy God, and to walk ever in his ways; then shalt thou add three more cities for thee, besides these three: that innocent blood be not shed in the midst of thy land, which Jehovah thy God giveth thee for an inheritance, and so blood be upon thee."

"Blood revenge was the police of the primitive Aryan and Semitic peoples."[7] It is important to notice that the Jews were not to change everything in their new place of residence. The ancient police system which featured the avenger of blood would continue to be used, but with the restraints and precautions inherent in the refuge system. In a similar way, the ancient landmarks in use for ages before Israel inherited Canaan were to be continued and honored. (See under Deuteronomy 19:14.) Under the avenger of blood system, any homicide gave the right to the next of kin to seek out the manslayer and kill him. In fact, it was considered a solemn duty for him to do so. The whole system of the cities of refuge was not designed to interfere with that arrangement at all, except in those cases where the killing was accidental, unintentional, and not premeditated.

In Deuteronomy 19:8,9, Moses instructed the people to set up three more cities of refuge, in addition to the six already commanded, IF God should enlarge their borders, as God had sworn to their fathers that he would do IF they remembered to keep all of God's commandments. Note that God's promise to enlarge their borders was conditional (Deuteronomy 19:9), and also that the instruction to appoint three more cities of refuge was conditional (Deuteronomy 19:8). The significant thing about these instructions is that it would have been impossible, long after the times of Moses, for anyone whomsoever to have included such orders as these! "No late author would have invented such a provision."[8] Not only did God never really enlarge Israel's borders until the times of David and Solomon, but even in their times, the conquered area was not really incorporated into Israel, but merely made tributary to Israel's monarchy, and furthermore, the conquered peoples quickly regained their independence when Solomon's incompetent son (Rehoboam) inherited the throne.

Oberst summarized the instruction regarding the cities thus: "The appointment of the six was WHEN, but the appointment of the other three was IF; and the job apparently never got done!"[9]

Deuteronomy 19:4-7 lays out instructions for the unintentional manslayer; and Deuteronomy 19:5,6 gives an example of what was meant by unintentional. Also, in Numbers 35:26-24, there are other examples of inadvertent homicide.