Exodus 20:13 - Matthew Poole's English Annotations on the Holy Bible

To wit any man or woman, without authority, and without just cause; which exception must necessarily be understood, because many other scriptures command the magistrate to kill great offenders. And this prohibition being delivered by God, who made, and searcheth, and commands men's hearts, must be extended not only to the external act of killing, but to all motions of the heart or tongue which tend that way, as anger, hatred, envy, malice, strife, blows, and the challenges of duelists; which is clearly manifest by comparing this with other scriptures, as Matthew 5:21 1 John 3:15, &c. And here, as in the rest, is commanded the contrary duty of preserving tie lives of our neighbours as much as lies in our power.