How should we understand the killing of sinful people in the Old Testament through the lens of the Gospel?
As we come to understand the definition of murder to be: the killing of a human being apart from the instruction and authority of God, there is certainly a lot to consider. In this past Sunday’s sermon, we covered how this definition of murder has implications for various situations like: physical acts of murder, hatred, anger, abortion, death penalty, law enforcement, military/wars, euthanasia, accidental “manslaughter”, and more. Ultimately, one of the main conclusions that I wanted to make through Scripture, was that, any killing of another human being in the Old Testament was to be done first and foremost in fear of the LORD, and not for one’s own pursuit of personal vengeance or justice. When Israelites were commanded to stone someone or put them to death for their sin, it was to be done with great fear and trembling. Putting a fellow Israelite to death was not supposed to be a pleasurable experience for those casting the stones. It should have been an event filled with great sorrow, grief, and fear that they were doing the right thing in God’s eyes. The same goes for when God commanded Israel to utterly destroy their enemies in battle. The killing of women and children was not something that the Israelite soldiers would have wanted to do (hence whey they failed to do it so often, thus disobeying God), but they were to obey God in this way because of what those people of other nations represented: godlessness, unrighteousness, and sinfulness.
Psalm 106:34-39 illustrates pretty well what God wanted to save the Israelites from by having them destroy all their enemies:
34 They did not destroy the peoples,
as the Lord commanded them,
35 but they mixed with the nations
and learned to do as they did.
36 They served their idols,
which became a snare to them.
37 They sacrificed their sons
and their daughters to the demons;
38 they poured out innocent blood,
the blood of their sons and daughters,
whom they sacrificed to the idols of Canaan,
and the land was polluted with blood.
39 Thus they became unclean by their acts,
and played the whore in their deeds. 
God sought for Israel to he holy as He is holy. When we read about the killings of sinful people and nations in the Old Testament, we must remember that those killings were to be done in direct obedience to God, as He alone is the perfect Judge of human life. God’s people were never to take another person’s life into their own hands without consulting God about it first.
So this brings us to the overall purpose of what I am writing to you about; How should we understand the killings of sinful people in the Old Testament through the lens of the Gospel?
Let’s take a look at Scripture:
43 “You have heard that it was said, ‘You shall love your neighbor and hate your enemy.’ 44 But I say to you, Love your enemies and pray for those who persecute you, 45 so that you may be sons of your Father who is in heaven. For he makes his sun rise on the evil and on the good, and sends rain on the just and on the unjust. 46 For if you love those who love you, what reward do you have? Do not even the tax collectors do the same? 47 And if you greet only your brothers, what more are you doing than others? Do not even the Gentiles do the same? 48 You therefore must be perfect, as your heavenly Father is perfect.
Here we see that Jesus commands His disciples to love their enemies. This would have been shocking to hear for them since much of Israel’s history was all about hating their enemy nations that were attacking them. In addition, King David is recorded many times in the Psalms literally praying for the destruction of those who are against him. So what does Jesus mean now when He says we are to love our enemies?
We need to take a closer look at how He ends this teaching when He says, “You therefore must be perfect, as your heavenly Father is perfect”. The perfect love of God is the only kind of love that knows how to love its enemies (Romans 6:23). Furthermore, I believe Jesus is preparing His disciples for the new era that is about to begin with His resurrection, when He says to His disciples, “Go and make disciples of all the nations…”. The Jews who follow Jesus are no longer supposed to view people of other nations as their enemies, because they will be tasked to take the Gospel message to them. Jesus first ministered to the Jews, and then the Gentiles/Greeks. The Apostle Paul echoes this pattern when he states how the Gospel is salvation to all those who believe, first to the Jews, then to the Greeks (Romans 1:16).
If we are not to hate other people, then what made it okay for the people in the Old Testament to kill those who were sinners? The answer to this question is better understood when we read in the New Testament how our hatred is to be directed.
Abhor what is evil; hold fast to what is good.
We are told to literally hate evil. This verse comes in the context of the importance of seeking to live at peace with those around us. Just as the Israelites in the Old Testament were to hate evil so much that it would not stop them from carrying out God’s justice against sinners, Christians today are to hate evil with the same intensity. However, we must be very careful that our hatred of evil does not translate into the hatred of another human being made in the image of God. So the next question would be, how are we to correctly hate evil?
I think Hebrews 12:1 says it well, “lay aside every encumbrance and the sin which so easily entangles us…” We should be constantly seeking the destruction of our sin that hinders us from living the holy life that God calls us to. Of course, we will never achieve that holiness until we are made new in our life in heaven, but our knowledge and understanding of God’s love for us through Christ is what fuels our desire for our striving after holiness.
The Apostle Paul writes a warning to the Corinthians in regard to the dangers of willfully living in sin, “Test yourselves to see if you are in the faith, examine yourselves! Or do you not recognize this about yourselves, that Christ Jesus is in you – unless indeed you fail the test?” (2 Corinthians 13:5).
When we have a holy hatred for sin, we are exercising a proper view of sin being our “enemy”. First Corinthians 15 calls the last enemy of God “death” (1 Corinthians 15:26), which is mentioned again in Revelation 20 when it foretells the future of death and Hades being thrown into the Lake of Fire. Furthermore, Paul writes clearly about death being the end result of sin (Romans 5:20-21), and so does James (the half-brother of Jesus) in his letter when he says, “…when lust has conceived, it gives birth to sin; and when sin is accomplished, it brings forth death.” (James 1:15).
So the next time you read a Psalm of David like this one regarding his enemy:
6 Appoint a wicked man against him;
let an accuser stand at his right hand.
7 When he is tried, let him come forth guilty;
let his prayer be counted as sin!
8 May his days be few;
may another take his office!
9 May his children be fatherless
and his wife a widow!
10 May his children wander about and beg,
seeking food far from the ruins they inhabit!
11 May the creditor seize all that he has;
may strangers plunder the fruits of his toil!
12 Let there be none to extend kindness to him,
nor any to pity his fatherless children!
13 May his posterity be cut off;
may his name be blotted out in the second generation!
14 May the iniquity of his fathers be remembered before the Lord,
and let not the sin of his mother be blotted out!
15 Let them be before the Lord continually,
that he may cut off the memory of them from the earth! 
We are no longer permitted to pray this way concerning other human beings, but we are obligated to pray this way concerning our own sinfulness and the sinfulness that is in the world. It should be the longing of our hearts to see this world seek after the righteousness of God and to place their faith in Christ for their salvation so that they would see their sin utterly destroyed on the cross.
When we read about the killings of sinful people in the Old Testament (God’s smiting, Israelites being stoned to death, enemy nations being destroyed), we must first remember that we are all deserving of death, in God’s perfect justice, but it is His grace and patience that allows us to continue to breath. For those who already fear God and have their faith firmly in Christ, each breath we take is to be done in worship to Him. For the unbelievers, every breath they take is another opportunity for them to repent of their sin and put their faith in Jesus for their salvation. Secondly, we must remember that we are to have the same level of the fear of God and hatred for sinfulness that we are willing to do whatever it takes to destroy sin in our lives for God’s name sake as the Israelites were supposed to have in the Old Testament. Lastly, when we read about the killing of sinful people in the Old Testament, it would be good for us to remember that it was Jesus, the Lamb of God, who died our death and paid our debt for the sins we have committed. He became sin who knew no sin, so that we might become the righteousness of God.