From the day the universe and man were created, it has been against the law of God for anyone to take the life of another with the exception of self-defense. There are not many references to this under the first dispensation know as the Partiarchal age. Those that are mentioned, makes it clear that God had not intended for it to be done. The story of the first two children born to Adam and Eve, brothers Cain and Abel, gives us the insight into how God feels about murder.
The story is familiar to most people but for those who may not be aware, we will give a brief listing of it. Cain, the oldest, we are told was a tiller of the soil. In other words he grew vegetables for food. Abel was a keeper of sheep. There is no background information listed as to why these two were following different lines of work. Possibly it was that Adam and taught them the two in order to help furnish the family with theri needs. Regardless of that, we can conclude that God had instructed them that they must offer animal sacrifices in their worship to Him. Cain, apparently felt that offerings from his produce would be satisfactory to God. Following is the brief story of what occurred.
And Adam knew Eve his wife; and she conceived, and bare Cain, and said, I have gotten a man from the LORD. And she again bare his brother Abel. And Abel was a keeper of sheep, but Cain was a tiller of the ground. And in process of time it came to pass, that Cain brought of the fruit of the ground an offering unto the LORD. And Abel, he also brought of the firstlings of his flock and of the fat thereof. And the LORD had respect unto Abel and to his offering: But unto Cain and to his offering he had not respect. And Cain was very wroth, and his countenance fell. And the LORD said unto Cain, Why art thou wroth? and why is thy countenance fallen? If thou doest well, shalt thou not be accepted? and if thou doest not well, sin lieth at the door. And unto thee shall be his desire, and thou shalt rule over him. And Cain talked with Abel his brother: and it came to pass, when they were in the field, that Cain rose up against Abel his brother, and slew him. And the LORD said unto Cain, Where is Abel thy brother? And he said, I know not: Am I my brother's keeper? And he said, What hast thou done? the voice of thy brother's blood crieth unto me from the ground. And now art thou cursed from the earth, which hath opened her mouth to receive thy brother's blood from thy hand; When thou tillest the ground, it shall not henceforth yield unto thee her strength; a fugitive and a vagabond shalt thou be in the earth. And Cain said unto the LORD, My punishment is greater than I can bear. Behold, thou hast driven me out this day from the face of the earth; and from thy face shall I be hid; and I shall be a fugitive and a vagabond in the earth; and it shall come to pass, that every one that findeth me shall slay me. And the LORD said unto him, Therefore whosoever slayeth Cain, vengeance shall be taken on him sevenfold. And the LORD set a mark upon Cain, lest any finding him should kill him. (Genesis 4:1-15 KJV)
Although God did not require the life of Cain in exchange for Abel's, His disdain for the slaying is quite obvious. Another killing took place some five generations later by an offspring of Cain. Lamech, who was the son of Tubal-cain. Lamech was the first man recorded as marrying more than one wife. And the following is a very brief account of his killing a young man:
Lamech said to his wives, "Adah and Zillah, Listen to my voice, You wives of Lamech, Give heed to my speech, For I have killed a man for wounding me; And a boy for striking me; If Cain is avenged sevenfold, then Lamech seventy-sevenfold." (Genesis 4:23-24 NASV)
Lamech refers to the protection God gave to Cain who killed in anger and suggests that, since his was self defense, anyone who took vengeance upon him would be avenged by God much more.
When the Israelites were miraculously freed from Egyptian bondage and God set them apart as His chosen people to furnish the lineage to the messiah, He gave Moses the ten commandments engraved in stone. Following that He gave Moses the entire Covenant law whereby they were set apart. In this law, the killing (murder) of another person was strictly prohibited. I was even one of the ten basic commandments, plus given in minute detail within the covenant body.
In Exodus chapter 21, we find the details and circumstances explained, plus other factors concerning the law. It is strongly suggested that the reader, go to the link of chapter 21 and read it carefully. It not only describes the circumstances whereby one must be put to death in retribution for murdering another, but it also describes the six cities which Moses must set apart as 'cities of refuge'. These were to be established in order for someone who may have killed accidentally or in self defense, might get a fair shake.
In addition to Exodus 21, there are other scriptures which itemize the 'eye for an eye' principle. Here is one such:
“And if a man cause a blemish in his neighbour; as he hath done, so shall it be done to him; Breach for breach, eye for eye, tooth for tooth: as he hath caused a blemish in a man, so shall it be done to him again.” (Leviticus 24:19-20 KJV)
In connection with this same rule, we find circumstances detailed in a number of passages:
When the LORD thy God hath cut off the nations, whose land the LORD thy God giveth thee, and thou succeedest them, and dwellest in their cities, and in their houses; Thou shalt separate three cities for thee in the midst of thy land, which the LORD thy God giveth thee to possess it. Thou shalt prepare thee a way, and divide the coasts of thy land, which the LORD thy God giveth thee to inherit, into three parts, that every slayer may flee thither. And this is the case of the slayer, which shall flee thither, that he may live: Whoso killeth his neighbour ignorantly, whom he hated not in time past; As when a man goeth into the wood with his neighbour 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 neighbour, that he die; he shall flee unto one of those cities, and live: Lest the avenger of the blood pursue the slayer, while his heart is hot, and overtake him, because the way is long, and slay him; whereas he was not worthy of death, inasmuch as he hated him not in time past. (Deuteronomy 19:1-6 KJV)
One thing which may confuse the reader. When the Israelites where approaching the promised land of Canaan, they encountered opposition from some of the established nations along their way and were forced to fight them. In so doing they took control of considerable territory. These lands were located on the eastern side of the Jordan river whereas the land of Canaan was comprised of several nations on the western side of Jordan. The tribes of Reuben and Gad, desired to stay on the east side and agreed that the men would go over with the rest of the Israelites and help take those lands and then return to their own. And half the tribe of Manasseh also remained on the east side. There were to be six cities of refuge, three on the east side of Jordan and 3 on the west side.
When one party killed another, if murder, 'the avenger of blood' was a close relative of the dead man and under the law, he was authorized to kill the assailer. The cities of refuge gave the killer an opportunity to present his case.