The answer to this topic may seem pretty straightforward. But there are some things we need to emphasize, meaning this subject requires a bit more thought than perhaps realized.
War is nothing we should ever take pleasure in because it is a sad result of the curse of sin passed down from Adam.
The commands to Israel in the old testament are not valid for believers today
First, we must be cautious when using examples of Israel from the Old Testament because we (the modern church) live and operate under the new covenant. We are not Israel and should use extra precautions not to make applications from commands not valid for us today. Israel’s holy wars were permitted by God (perfectly just and fair) and were necessary for the salvation of many through the preservation of His ambassador Israel. But our question involves the believer’s present application under the new covenant. So we are not here to discuss Israel’s past encounters with her enemies. If the Lord commanded them to go to battle, then they were to obey. If they were not commanded (and perhaps even forbidden directly), they were to refrain from advancing (Deuteronomy 1:41-45). But again, this was in Israel’s old days and is not comparable to our modern time when a citizen of a particular country voluntarily agrees to serve their nation (we will explain more of this below). The New Testament has nothing to say about Christians entering the military (assuming they see combat). But the reason for this is because (like many other topics) we are to use a little common sense and figure these things out for ourselves.
When we say “believers going into the military,” we assume these individuals will be involved in actual combat that consists in killing other people. There are plenty of jobs in the military that don’t include this (hence we specified here).
Not all so-called “holy wars” throughout history were justifiable or approved by God
Before we continue, we should briefly mention that not all “holy wars” throughout history were in fact so. So we must carefully differentiate the good from the bad. The Crusades are probably one of the best examples of unrighteous conflict never permitted by God simply because they were driven by secular and humanistic means and purposes. There was no divine revelation and communication whereby the people involved had anything to go by, as did Israel. Those who participated in the movements known as the Crusades had no divine approval to do what they did. Worse, they were ultimate failures that accomplished very little (if anything). We could continue with a handful of other examples (whatever they may be) of unrighteous acts committed by those who took matters into their own hands. But time and space will not permit and that is not the point of our discussion. The fact is that not all war is justifiable.
It is not sinful for believers to serve their country and kill in a war generally speaking
With the above out of the way, is it sinful for believers to serve their country and kill in a war? The general answer is no, but this can depend. We have already discussed elsewhere that it is pointless and a bad idea for believers to run for office or involve themselves in politics. So since we aren’t here to make the world a better place, someone may ask, “why would serving in the Military be less of a waste of time?” But there are many distinct differences between the two (the military and politics). Joining a nation’s defense system does not pose the same spiritual risks that political involvement present. For the sake of time and explanation, I encourage the reader to see “Believers and Politics.” The information contained there should easily suffice to inform the reader of the vast differences between the two. First, however, we must mention that today’s military (especially in the United States) has become more politically involved than ever before (woke, as they call it). But that does not mean any believer wishing to serve their nation has to involve themselves in those activities. There is nothing wrong with wanting to give back to one’s country through serving in the armed services just as long as the individual in question realizes that this won’t change the world for the better (make heaven on earth). After all, our men and women in service make the freedom (and all other luxuries) we enjoy possible. Volunteering for service is one way to show gratitude for the good they do for us.
Additionally, some countries enforce mandatory service by drafting whomever they see fit to join the ranks of those in defense of their nation. We are to submit to the government as long as they aren’t asking us to do anything unbiblical (Romans 13:1-7). However, in countries where this is not mandatory (the United States as an example), we should never create this idea that “all able-bodied men and women should serve time in the military.” That is pure legalism based on nothing. We are all called to different things, something those within the body of Christ should understand better than anyone.
Civilians and non-civilians need to respect one another
Additionally (as a quick side discussion), it is not uncommon for some to experience an attitude of contempt and scorn from either civilians or veterans toward themselves. As time has gone by (especially here in the United States), the civilian populace has become ever increasingly ungrateful and disrespectful to those who have sacrificed so much for the freedom they now enjoy (clearly a sign of the times we live in today). That is not how believers should behave toward those who have justifiably given up so much.
On the other extreme of this issue is how some in the military sometimes wrongly look down on civilians in general (even if they haven’t been disrespectful). The reason is that many civilians are deemed ungrateful for the service and freedom they receive and ignorant of all the pain and suffering endured to grant it. While it is true that this is the case with many who have never experienced what they did, not all non-military individuals are like what we’ve described above. It is not right to throw most or even all people into one category. Christians should never carry that attitude (especially since we all suffer in different ways and have our own life-stories to tell). And besides that, all believers will already have enough suffering to endure throughout their lives so that the experiences and circumstances of others (those never in the military) should not be downplayed as unimportant or inferior. That would be hypocritical. We should never assume we know what everyone else has been through without getting to know them personally. The degree of challenges we must all endure will vary, and they are all important to God who knows sorrow and suffering better than any of us. The entire chapter of Isaiah 53 should suffice to get the idea drilled into our heads. Due to its length, we will leave only a small portion of it below.
Who has believed our message and to whom has the arm of the Lord been revealed? 2 He grew up before him like a tender shoot, and like a root out of dry ground. He had no beauty or majesty to attract us to him, nothing in his appearance that we should desire him. 3 He was despised and rejected by mankind, a man of suffering, and familiar with pain. Like one from whom people hide their faces he was despised, and we held him in low esteem.4 Surely he took up our pain and bore our suffering, yet we considered him punished by God, stricken by him, and afflicted. 5 But he was pierced for our transgressions, he was crushed for our iniquities; the punishment that brought us peace was on him, and by his wounds we are healed.
So even if the suffering endured by those in war may be greater than that tolerated by others, this is not always the case and never justifies making sweeping judgments about other people. There is no excuse for one professing to know the Lord not to accept this. The point is that we should never carry a superiority complex (no matter how noble one’s career may be). Plus, we must remember that we believers are fighting a spiritual war playing out on an invisible battlefield. And the more one wishes to please their true Master, the more opposition they will receive (resulting in greater suffering that must be endured). The individual maturity level of each and every believer must be considered even if that is something we can never know for anyone (only God knows). All we need to know (and can) is that everyone is at different levels.
You therefore, my son, be strong in the grace that is in Christ Jesus. 2 The things which you have heard from me in the presence of many witnesses, entrust these to faithful people who will be able to teach others also. 3 Suffer hardship with me, as a good soldier of Christ Jesus. 4 No soldier in active service entangles himself in the affairs of everyday life, so that he may please the one who enlisted him.
Understandably, we would be correct to see wrong in any ungratefulness (and what have you) toward those who sacrificed so much in serving their country. But we must never allow this to lead to any hate (Jesus tells us to love all men, even our enemies Matthew 22:37-39, 5:43-45). And it would be highly misguided (not to mention judgmental Matthew 7:2) to lump all civilians together as if they are somehow all the same. Soldiers are no better than anyone else. What other reason is there that ones serves their country if not out of love (a country is not a land but a people)? No, this doesn’t mean we have to agree with everyone’s attitude or even like them. But we should never hate anyone and put them all into the same category. There are plenty of people who are not like that serving in honorable ways themselves (even if not in the military). It is never right to look down on others, especially if we don’t know them personally (their attitude, goals, interests, beliefs, spiritual gifts, calling, and whatever else you may have).
However, believers should possess great gratitude and a fair level of respect for those who serve (have served) the country they live in. As the saying goes, “freedom isn’t free.” But we know that God has a different plan and calling for everyone and that the only work that will last (the only work that truly matters) is that done for the spiritual good of others. To obey the Lord and do what He would have us do is far better than any secular career (by itself).
More on whether it is wrong to engage in war and kill others
Now to continue our discussion, should a believer fight in a war? First, the individual needs to make sure they are following the Spirit’s leading. It is unwise to pursue a path the Lord doesn’t want us to take (Proverbs 3:5-6). The short answer is that joining the military is not wrong in and of itself. God does call many believers to that path. So what of those who jump into something God wasn’t leading them to? The most we can say is that doing such a thing is not a good idea.
The next question we need to address involves taking the life of other people. The answer to this has variables because it can depend on the time and circumstances. There are (as we all know) such things as “war crimes,” which may consist of wrongfully taking other people’s lives. The circumstances can make deciphering this difficult for those unfamiliar with the proper military code of conduct (whichever country one hails from). However, this is not something believers need to worry about because the Lord would never allow us to be tested beyond what we can handle (1 Corinthians 10:13).
Some things should not be done in war. More challenging yet are situations that would fall into areas of application (whatever they may be). But separating the two is something the Lord will grant every believer the ability to do if a difficult situation presents itself. Again, it will not be too much for the brother or sister’s faith to handle.
It is not sinful to kill in a war that involves the defense of one’s country. So some are justified when violence is necessary to defend themselves and others. Different nations could not exist without a defense system (we also have border security and Laws for crime for similar reasons). And this is no small point because God instituted nationalism (whatever word one wishes to use to describe God’s actions in Genesis 11:1-9) for a reason. Suppose one country seeks to annihilate or enslave the inhabitants of another (you could think of Nazi Germany as an example). In that case, to preserve what God formed, countermeasures are necessary (many countries will form alliances and come to the defense of others). However, there are times to fight and times to submit (Ecclesiastes 3:2-5).
For example, the persecution of Christians by the Roman authorities under the various emperors indirectly mentioned in the Lord’s message to Smyrna (Revelation 2:8-11) would have been (for believers) an inappropriate time to start a war and fight back. That is one example, and one involving an attack against the church. Another, though unrelated in its type and nature, was the crusades. They did not involve the direct persecution of believers but something else. It would have been (and was) sinful to engage in such an unauthorized movement through criminal violence. We can also think of the Roman occupation of Israel in Jesus’s day and how useless it was/would have been even to attempt to overthrow a nation (one far more powerful) used by our Lord as a “whip” of discipline. The Old Testament contains plenty of examples of God warning His people not to resist their oppressors or fight back. There was no point in resisting a stronger Gentile nation used by God to punish His people (which is why the Lord often told them to submit when it was clear their sins had finally overridden His patience).
The Tribulation will present a clear time when believers should submit to their oppressors (since this will involve a war of unbelievers (including the government) against believers). Would it be a sin to take up arms against the Beast’s henchman out to destroy us? Well, the very least we can say is that such would be a terrible idea and risk for the faith of the person(s) involved. To put it this way, banding together and declaring war against the Antichrist would be very stupid.
Are there doubts in the reader’s mind that involvement in any war (whether past, present or future) is sinful? There have undoubtedly been times (the Crusades were one of them) when this was the case, just as there have been plenty of unauthorized killings through unnecessary violence (war crimes). The answer to our question is that some war and killing are justifiable, while others are not. We need not wade into the details for reasons already touched on above. Suffice it to say here that the examples mentioned in our present examination should give us a good enough idea of the answer we have come to.