In Exodus 20:13 we read "Thou shalt not kill."
It seems that this would be the easiest commandment to keep as, morally, we know killing is not a righteous behavior. Even the law of the land, most lands, punishes murderers.
However, every day, we hear of gratuitous killings: some are perpetrated in the name of religion, some because of greed, pride, selfishness, others because of overzealousness in defending oneself, others for no other reason than to prove we can do it, and the list can go on.
Why has our Father in Heaven given us the commandment "Thou shalt not kill?"
In the Church of Jesus Christ of Latter-Day Saints, we believe that, before coming to earth, we lived with our Father in Heaven. There, we discussed the plan to come to earth that we might receive a body, grow, learn, and return home to Him because of the choices we would make.
The key word is "choose." He wanted to give us the choice of what we would do, what we would believe in, what destiny we would create for ourselves.
During this premortal discussion, there was one, Satan, who wanted to take away the possibility of choosing for ourselves. He wanted to just give us one road to follow, so that we would not go astray and be guaranteed a safe return to our heavenly home.
Heavenly Father and two thirds of His spirit children (all of us who came to earth) did not agree. We wanted the freedom to choose. Because of his rebellion, Satan was banished from His presence, along with his followers.
Life is a gift, and it is sacred, just as the ability to choose is an equally sacred gift.
Back to the question about the sixth commandment.
When a person is killed, his/her earthly life ends and so is the possibility of this person to grow, learn, and choose to return home to our Father in Heaven.
President Harold B. Lee explained: "One of the most serious of all sins and crimes against the Lord's plan of salvation is the sin of murder or the destruction of human life. It seems clear that to be guilty of destroying life is the act of 'rebellion' against the plan of the Almighty by denying an individual ... the privilege of a full experience in this earth-school of opportunity ..." (The Sixth Commandment, Part 1, The Ten Commandments Today, p 88.)
Every person that has ever lived, is living, and will live on this earth sided with our Heavenly Father and our Savior when they presented this plan.
If we could just remember this, perhaps we would try a little harder to follow Them and, perhaps, we would treat life with more respect and with the sacredness it deserves.