Why did the Old Testament command to kill? I've been reading the answers given in this similar question or even in the "duplicate question" but they don't respond to my question which is slightly different.  I'm not wondering if Killing is legit or not, but WHY God commanded to kill in the Old Testament.

This is a very common question asked by atheist as a way to show Bible inconsistencies and I believe the question and answers given in the previous questions are not exactly answering that.

I'm wondering why, in the first moment, God in the Old Testament was commanding to kill other people when in the New Testament killing is totally forbidden and Jesus never commanded it in any case.

It sounds like two different Gods: the aggressive one and the pacifist.

Some quotes from the old Testament commanding to kill are the following ones:

Leviticus 20:13 NAB


  "If a man lies with a male as with a women, both of them shall be put to death for their abominable deed; they have forfeited their lives."  


2 Chronicles 15:12-13 NAB


  They entered into a covenant to seek the Lord, the God of their fathers, with all their heart and soul; and everyone who would not seek the Lord, the God of Israel, was to be put to death, whether small or great, whether man or woman.


Exodus 22:17 NAB


  You should not let a sorceress live. 


Leviticus 20:27 NAB


  A man or a woman who acts as a medium or fortuneteller shall be put to death by stoning; they have no one but themselves to blame for their death.
Personally, I think that the primary difference is that the New Testament "gives to Caesar that which is Caesar's and to God that which is God's".  There is, in essence, in the Christian faith, a separation from what is legal and what is right in faith in Christ.  Whereas the Old Testament is both the law of God (those things that an individual should or should not do), which Christians still believe, and the law of the land of Israel (the legal consequences for disobeying the moral law).  Christians no longer adhere to the latter because they are dispersed among the nations (we don't stone people anymore for violating the moral law, we obey the legal system that is over us).  The same would technically be true of Jews. Jews are not stoning adulterers in the United States but allowing the United States' legal system handle those things.  Or if we prefer Biblical cases: Daniel did not stone the Babylonians for the evil they did when he was in Babylon.  Daniel kept to the moral law for himself...the law is good...but he did not pursue Israeli civil and criminal punishments against the Babylonians.

When Jesus refused to stone the woman caught in adultery, He did not say that the law against adultery was bad, and he did not say that stoning was wrong.  However, he did not stone the woman.  There seem to be two grounds for this: 1) It was against Roman law for them to stone the woman, and 2) Mercy and forgiveness are greater than the law of sin and death. While it is not wrong to punish someone for their sins, it is also not wrong to forgive, and forgiveness is greater. Pretty much the entire book of Romans will do more justice to this idea than I can give here.

Two additional things to note:


Jesus did not abolish the law (Matt 5:17).
Jesus did not lower the bar of morality but raised the bar.  Now lust is adultery (Matt 5:28), etc.


As to specifically killing.  In the United States, we do kill 1st degree murderers at times, and it's legal to kill in self-defense.  Many Christians support these laws and would kill in self-defense.  Though, some Christians like the Amish would not even kill in self-defense to my knowledge.

Ultimately, regardless of the laws of the land, the Christian is charged to do what is right, which is never illegal in any country:

"But the fruit of the Spirit is love, joy, peace, patience, kindness, goodness, faithfulness, gentleness, self-control; against such things there is no law." (Gal 5:22-23, emphasis added)