He that smiteth a man, so that he die, shall be surely put to death.

Matthew Henry's Concise Commentary

21:12-21 God, who by his providence gives and maintains life, by his law protects it. A wilful murderer shall be taken even from God's altar. But God provided cities of refuge to protect those whose unhappiness it was, and not their fault, to cause the death of another; for such as by accident, when a man is doing a lawful act, without intent of hurt, happens to kill another. Let children hear the sentence of God's word upon the ungrateful and disobedient; and remember that God will certainly requite it, if they have ever cursed their parents, even in their hearts, or have lifted up their hands against them, except they repent, and flee for refuge to the Saviour. And let parents hence learn to be very careful in training up their children, setting them a good example, especially in the government of their passions, and in praying for them; taking heed not to provoke them to wrath. Through poverty the Israelites sometimes sold themselves or their children; magistrates sold some persons for their crimes, and creditors were in some cases allowed to sell their debtors who could not pay. But man-stealing, the object of which is to force another into slavery, is ranked in the New Testament with the greatest crimes. Care is here taken, that satisfaction be made for hurt done to a person, though death do not follow. The gospel teaches masters to forbear, and to moderate threatenings, Eph 6:9, considering with Job, What shall I do, when God riseth up? Job 31:13,14.