What does the Bible say about the commandment 'thou shalt not kill'?

In Matthew 5:21-26, Jesus clarifies the commandment 'thou shalt not kill,' emphasizing that it is not only the physical act of murder that breaks this law but also the anger and hostility that may reside in our hearts toward others. He reveals that the spirit of the law demands love and reconciliation, suggesting that being angry without cause puts one in danger of judgment. This condemnation for inner sins highlights the importance of understanding the law as a spiritual requirement, showcasing God's unchanging demand for righteousness not merely as outward behavior but as internal holiness.