Exodus 20:13 which should read, “You shall not MURDER” (NASB or NKJV). The word “murder” is the Hebrew word ‘RATSACH’ which refers to the “unlawful taking of a human life.” Killing is not murder if one is executed for MURDERING someone.  KILLING is JUST in these cases, as we shall now see.

In Genesis 6:5, 11, 13 we read, “Then the LORD saw that the wickedness of man was great on the earth, and He was grieved in His heart… The earth also was corrupt before God, and the earth was filled with violence… And God said to Noah, ‘The end of all flesh has come before Me, for the earth is filled with violence through them: and behold, I will DESTROY THEM with the earth.” The Lord sent a universal flood, and everyone was KILLED except for Noah and his family. Men deserved to die, so this was a JUST ACT.

After the flood, God instituted “capital punishment.” We see this in Genesis 9:5-6, “Surely for your lifeblood I will demand a reckoning; from the hand of every beast I will require it, and from the hand of man. From the hand of every man’s brother I will require the life of man. ‘WHOSOEVER SHEDS MAN’S BLOOD, BY MAN HIS BLOOD SHALL BE SHED; for in the image of God He made man.” If one MURDERS someone, “taking their life” is an act of JUSTICE. In Romans 13:1-4 we see that God uses “governing authorities” to be the EXECUTIONERS OF MURDERERS. “Let every soul be subject to the governing authorities. For there is no authority except from God, and the authorities are appointed by God. Therefore whoever resists the authority resists the ordinance of God, and those who resist will BRING JUDGMENT UPON THEMSELVES. For rulers are not a terror to good works, but to evil. Do you want to be unafraid of the authority? Do what is good, and you will have praise from the same. For he is God’s minister to you for good. But if you do evil, be afraid, for HE DOES NOT BEAR THE SWORD IN VAIN; for he is God’s minister, AN AVENGER TO EXECUTE WRATH ON HIM WHO PRACTICES EVIL.”

Now let’s consider what you referred to (God ordering Israel to wipe out nations). We will read Exodus 17:14 first: “Then the LORD said to Moses, ‘Write this for a memorial in the book and recount it in the hearing of Joshua, that I WILL UTTERLY BLOT OUT THE REMEMBRANCE OF AMALEK from under heaven.” Now let’s read 1 Samuel 15:1-3, “Samuel also said to Saul, ‘The LORD sent me to anoint you king over His people, over Israel. Now therefore, heed the voice of the words of the LORD. Thus says the LORD of hosts: I will punish Amalek for what he did to Israel, how he ambushed him on the way when he came up from Egypt. Now go and attack Amalek, and UTTERLY DESTORY ALL THAT THEY HAVE, AND DO NOT SPARE THEM.’” Here is a case where a nation had, without any mercy, ambushed the children of Israel as they journeyed to Canaan. Their intent was to “wipe Israel off the face of the earth,” even though Israel had done nothing to deserve their wrath. They were the avowed enemies of Israel and thus God, in His HOLINESS, determined to JUDGE THEM. He used Isreal to be their EXECUTORS. This, too, was NOT a case of UNLAWFUL MURDER, but of a case of RIGHTEOUS JUDGMENT.

Regarding God’s mercy, God can and does show MERCY to men, but He can’t show mercy without also being JUST. All men deserve judgment (see Romans 3:9-19, 23; 6:23a with Hebrews 9:27), but by God’s mercy He saves men “through Jesus Christ our Savior” (Titus 3:5-6). Jesus Christ had to go to the cross to take our place in DEATH and JUDGMENT to pay for our sins and now God can be “JUST and the JUSTIFIER of the one who has faith in Jesus.” At the cross, “Mercy and truth have met together; righteousness and peace have kissed” (Psalm 85:10). And thus we read in Romans 5:20-21, “But where sin abounded, grace abounded much more, so that as sin reigned in death, even so grace might reign through righteousness to eternal life through Jesus Christ our Lord.”  (DO)  (738.3)