"THOU shalt not kill" (Ex. 20:13) covers a wider field than is indicated in the technical sense of murder, the premeditated slaying of a human being.
The earliest Biblical mention of such an act appears in the allegorical account of Cain's mortal attack upon his brother, Abel. In the allegory a menacing background of evil thought is shown as precipitating violence and destruction.
These two young men are pictured as living in a pastoral environment. Cain, the elder, raised crops, while his brother turned his attention to the keeping of sheep. There is no mention of any contention between them, until each brought an offering to the Lord. Abel's offering of some lambs was accepted, while that of Cain, who presented the produce of his fields, was apparently ignored. Whatever the reason for this rejection, anger and resentment flared up in Cain's thought, and he slew Abel (see Gen. 4:8)—an act leading swiftly to stern rebuke and perpetual banishment ordained by the very God whose favor Cain had sought to receive.
