You shall not kill (Ex 20.13; Deut 5.17, NAB). You have heard that it was said to men of old, “You shall not kill: and whoever kills shall be liable to judgment.” But I say to you that every one who is angry with his brother shall be liable to judgment (Mt 5.21-22, NAB).
You shall not kill is not just a metaphor. In the societies of biblical times, killing someone else for their land or possessions was a common occurrence. God admonishes us not to kill because to God each life is his precious gift and not man’s to take away. In the days of the American west, stealing someone’s horse was a capital crime. At first glance, this seems unduly harsh until you understand that a man without a horse was certain to die either from the harsh environment or from the hostility of the people around him. Thus, the horse thief was killing the victim either directly or indirectly. In today’s job market, putting someone’s ability to earn a living at risk so that we can gain a short-term advantage isn’t much different than stealing a horse was in the American west.
Read what our Lord God said to Moses in Leviticus 19.1-2, 11-18: The LORD said to Moses, "Speak to the whole assembly of the children of Israel and tell them: Be holy, for I, the LORD, your God, am holy. You shal not steal. You shall not lie or speak falsely to one another. You shall not swear falsely by my name, thus profaning the name of your God. I am the LORD."
"You shall not defraud or rob your neighbor. You shall not withhold overnight the wages of your day laborer. You shall not curse the deaf, or put a stumbling block in front of the blind, but you shall fear your God. I am the LORD."
"You shall not act dishonestly in rendering judgement. Show neither partiality to the weak nor deference to the mighty, but judge your fellow men justly. You shall not go about spreading slander among your kin; nor shall you stand by idly when your neighbor's life is at stake. I am the LORD."
"You shall not bear hatred for your brother in your heart. Though you may have to reprove him, do not incur sin because of him. Take no revenge and cherish no grudge against your fellow countrymen. You shall love your neighbor as yourself. I am the LORD."