As I study the Scriptures, I see no dispensation where God has ever approved of an individual taking vengeance into his own hands if he has been wronged in some way. Leviticus 19:18 reads - "You shall not take vengeance, nor bear any grudge against the children of your people, but you shall love your neighbor as yourself: I am the LORD." Psalm 94:1 is clear that vengeance belongs to God. Romans 12:19 - "Beloved, do not avenge yourselves, but rather give place to wrath, for it is written, 'Vengeance is mine, I will repay,' says the LORD." However, these verses must be harmonized with other Scriptures, for example, Numbers 31:1,2 - "And the LORD spoke to Moses, saying, 'Take vengeance on the Midianites for the children of Israel."
How can God forbid vengeance and then command it? It would seem that although vengeance belongs to God, He may authorize humans to implement it on His behalf. This explains how God could grant permission to a close relative to take vengeance on a murderer (cf. Num. 35:9ff) and there be no conflict with Leviticus 19:18. If God authorizes an evil doer to be put to death--either by an avenger of blood or, in our case today, civil government--it is the LORD Himself who is taking vengeance! Recall that Paul called civil authority "God's minister" (Rom. 13:4), and this is one way in which he serves: administering God's vengeance against evil doers. Let me be clear: To take matters into your own hands and "get even" as an individual is wrong, but when God authorizes vengeance to be meted out (against an individual or nation), it is proper and good for that punishment to be implemented by the authorized agent of God.
So, if I lived under the Mosaic age, it would be right for me to execute God's vengeance against one who murdered a close relative of mine (after due process is granted in a city of refuge, of course). In so doing I would be complying with God's law. I would not be taking personal vengeance; I would be administering God's vengeance in His prescribed way. However, today, in order to comply with God's law in the Christian age, I must allow civil authorities to punish evil doers. God has put that responsibility upon them. In other words, government is God's authorized "avenger of blood" today. In either situation, God is punishing the evildoer through His authorized servant.
Let us now give brief attention to some objections offered against the death penalty and also supply a basic response to each:
1. "Capital punishment is cruel and unusual."
It is true that the death penalty is unusual today; it is rarely used. Nevertheless, that doesn't make it wrong. Is it cruel for the state to take the life of someone who has committed a violent crime and been cruel to other human beings and their families? I do not believe so. There are humane ways to end a physical life. The bottom line is this: God authorizes government as His minister to punish evil doers, including using the death penalty. If a state does not want to execute that right, then that is their choice, but, in so doing, they are not relieved of their duty to execute wrath against the wicked.
2. "Capital punishment denies due process of law."
Although the death penalty is irreversible, it does not deny due process of law. If I were falsely imprisoned for 20 years, that is irreversible also. I'll never get those 20 years back! Ultimately, Bible believers understand that this life is not the final arena for justice. Mistakes, no doubt, happen when it comes to issuing fines, imprisoning, and implementing capital punishment. The fact that our judicial process is not perfect is not a rationale to let criminals do as they please without appropriate punishment. Government should do the best it can to uphold what is good and punish what is evil, even if they make mistakes in so doing.
3. "The death penalty is not a viable form of crime control."
From what I understand, some studies come to different conclusions on this. However, Solomon explained the deterrence issue very clearly over 3000 years ago in Ecclesiastes 8:11 - "Because the sentence against an evil work is not executed speedily, therefore the heart of the sons of men is fully set in them to do evil." Of course there is no observable deterrent factor in our country when murderers are imprisoned for 15 or 20 years first! That is not speedy justice! Additionally, it is a fact that the death penalty is 100% effective in preventing more violent crime from the one being executed! Prison time certainly does not guarantee this.
4. "A society that respects life does not deliberately kill human beings."
That's quite an argument coming from our culture. Our nation aborts over a million human beings a year! There is no comparison between a woman murdering her child out of personal convenience and God's authorized minister (civil government) executing wrath on evil doers. The latter is approved by God; the former is not.
5. "We are to pray for our enemies, not kill them."
Jesus was discussing the ethics of personal conduct when He said we should pray for our enemies and not retaliate (cf. Matt. 5:38ff). But this does not negate the role of civil government as God's minister (cf. Rom. 13:4). Even under the Old Testament, the individual was to love and not take matters into his own hands personally (cf. Lev. 19:18), but that didn't negate the proper administration of vengeance through God's approved instrument. Though it is beyond the scope of our current study, there is nothing wrong with a Christian serving as a policeman or soldier today (though some may have conscience issues, which must be respected). There is only one gospel and all are amenable to it. The teaching that authorizes a non-Christian to serve the state (even to the point of using lethal force) authorizes the Christian to serve the state in the same capacity.
6. "Life in prison provides more time for the wicked to repent, which is a good thing."
It is true that life in prison would provide more time for the wicked to repent. Of course, "life in prison" really isn't "life in prison" much of the time. There is often a chance to get out at some point, and sometimes more heinous crimes are committed after release. That never happens with the death penalty. However, the real point to stress here is that if God desired more time for all men to repent--even those who commit terribly wicked crimes--then why did He authorize the death penalty for civil government today? Why did He authorize it at all? Whatever answer can be given to that question will also suffice to answer this objection.
Let's conclude this study with a powerful quote from over 30 years ago from Rubel Shelly:
"Let God's people be peace lovers and peace makers in society. Let us pray for an easing of tensions and the elimination of wars among nations. But, may we not be so naive as to think that permissive attitudes and minimal punishments are the means to such stability. God has ordained civil governments to function for the good of its citizens by opposing evil in a firm manner. May we give ourselves to the support rather than the discouragement of that role. So long as sin is in the world, the lusts of the wicked will create wars (James 4:1); so long as Satan works his way in the hearts of men, there will be rape, murder, and other horrible crimes of man against his fellow man. It is not the will of God that good men and good causes be trampled underfoot in the onrush of such wickedness. He has ordained a ministry to oppose, fight, and crush crime in society. And, while Christians find no delight in war or the death of the ungodly, we realize that some people forfeit their right to life in society by their deeds. Just as God himself takes no pleasure in the death of anyone (Eze. 18:32) - not even the death of the wicked (Eze. 33:11) - yet, has destroyed many, so must the children of God adopt an attitude of sorrowful duty in carrying out the divine edict in the vengeance taking work of civil government. It is not pleasant, but it is right."