The meaning of the Sixth Commandment?

Thou shalt not kill. (Exodus 20:13 KJV)

You shall not murder. (Exodus 20:13 ESV)

British Family Bible

Thou shalt not kill. In this sixth commandment, which concerns man’s life, it is forbidden to commit these sins:

1. Hatred; 1Jo 3:15.
2. Causeless and revengeful anger; Mt 5:21-22.
3. Grievous reproaches; Ps 64:3.
4. Occasion of bloodshed; De 22:8.
5. Contrivance of man’s death; 2Sa 12:9.
6. Actual and willful murder. Ex 21:14.

In the same 6th commandment is enjoined the preservation of man’s life;

1. By a seasonable and moderate use of God’s creatures ordained for that end; Ec 10:17; 1Ti 5:23.
2. By a prudent avoiding of dangers; Mt 10:23.
3. By avoiding all sins; and particularly murder and uncleanness, Ps 55:23, which are noted to be especially destructive to the body and soul of him that commits them; Pr 5:11; Pr 6:32. Oxford Catechism.

kill. Killing in some cases is not murder; nor forbidden by God: such as the execution of justice, after a lawful manner, for a suitable offence, and by a lawful magistrate; the necessary defense of a man’s own life: to which under the law were added some other cases, with which we are not concerned now under the Gospel. Abp. Wake.

Family Bible Notes

Not kill; nor take the life of any human being, except when God requires it. Ge 9:6; De 25:17-19; 1Sa 15:1-3, 1Sa 15:18-19. This command forbids not only murder, but all those practices and kinds of business which tend to destroy human life; but the commandment rather requires the performance of those duties, and the pursuit of the courses that tend to preserve human life and render it useful.

By taking the life of a human being when not required by God, a man forfeits his own, and ought, in obedience to the divine requirement, to be put to death.