The Bible is filled with God-honoring military members. It's clear that the military can be a noble profession for a believer; it is not against the Bible to be a member of the armed forces of a legitimate, sovereign nation. God put civil authorities in place to rule mankind. Part of that responsibility is military defense. It is biblical for nations to defend themselves through warfare.
Should a Christian join the military?
Arguments that joining the military is akin to murder reflect political beliefs, not biblical beliefs. First of all, although the King James Version says, "Thou shalt not kill" as the Sixth Commandment, the better translation is "Thou shalt not murder." That does not apply to most wartime situations. It's popular among more liberal Christians (and Quakers) to categorically condemn war and the military. However, such a position is not a biblical concept, and to claim otherwise is deceptive.
Of course, that doesn't mean that joining the military is the right choice for everyone. There are some serious questions that should be addressed before anyone chooses to join the armed forces.
Can you in good conscience swear to and abide by the enlistment/commissioning oath?
A good military oath will demand loyalty to the nation and possibly the law and/or constitution of the nation. A bad oath will pledge allegiance to a specific leader. The German oath includes promises to serve the country and defend the law and the freedom of the German people. The Polish army pledges to serve and defend the country, guard the constitution, and preserve the honor of both the soldier and the military forces. The U.S. enlisted oath does not mention defending the nation, but does pledge to defend the constitution and obey the lawful orders of the president and officers in command. The officer oath is similar, but vows to serve well and faithfully, instead of following orders. Although Jesus admonishes us to be of such character that oaths are not necessary, military branches often require them for service. If you can't make such an oath willingly and with the full intent to keep it, military service probably isn't a good idea.
Are you willing to support the geopolitical leanings of the nation with your life?
The authorities of a nation have the God-given right to defend their nation. Soldiers under that authority are in their rights to kill—as long as they do so legally (generally, according to the Geneva Convention). This, for the most part, morally absolves soldiers of guilt in regards to legitimate wartime violence. But before the fight begins, before the person even joins the service, he needs to be able to say, "Yes, I trust that, in any situation my country puts me, I can follow orders with no great hesitation." A little hesitation is normal—any job is going to have odious tasks. And allegiance to a nation does not mean absolute understanding and support of every order. A believer should reconsider before swearing to fight for an abusive and corrupt regime or one that sends him into a war he absolutely disapproves of.
Can I be, or do I have a problem with being, a person who has killed another?
For many, this question doesn't even come up until after the deed is done, but it's a good idea to think about it beforehand. Most militaries have non-combatant roles such as chaplains, medical personnel, and many other career fields that may never directly engage the enemy. But the military is still in the business of death, and every support job, eventually, works in support of a weapon. In addition, the needs of the military will outweigh any promised job position. For example, if no combat officers are free to provide armed escort for a supply caravan, a logistical officer may very well be called up instead. (See Judges 4:17-22.)
Is the military life something I and my family can accept?
There are many advantages to having a family in the military. They will get to travel to different places, meet new people, and usually not have to worry about income. But every family needs to decide if the benefits are great enough to outweigh the disadvantages. Travel to visit extended family is expensive. The military member will often not have a choice of assignments. Spouses and children may not want to move or may be fearful of every new deployment. A commitment is a commitment. A five-year commitment doesn't change if you meet and marry the love of your life within the first two years. You still have three years to serve, and much of that may be deployed.
What is my motivation for joining the military?
Often, the military can provide regular income, advanced education, and medical care. It is not uncommon for a poor high school student or someone with an ill spouse or child to see the military as an answer to his needs. And it is not necessarily bad to consider the military for these reasons. But the other questions should still be considered. Is health care or a college degree worth spending eighteen months in a foreign country being shot at? Is it worth spending eighteen months shooting back? Is it even possible to work toward a degree while being deployed every other year? For many, the benefits are worth the risk and inconvenience, and military retirement may one day free a family for ministry. But it's a question that each individual and family should answer for themselves.
What about mandatory military service?
In some countries military service isn't an option; it's mandatory. In that case, to serve is to obey the civil authorities God has placed in power. If, however, a Christian is conscripted into the military of an evil regime, he should make every effort to find a noncombatant role or determine if there is a legitimate cause for civil disobedience. Also, he should pray for wisdom and trust that God can glorify Himself in any situation.
A Christian considering the military should prayerfully consider these questions and then follow the Holy Spirit's leading. Strong, Spirit-filled believers are needed in the military, just like they are needed in every other field of endeavor. Military service is an honorable option, but, in most cases, it's only one option.
Does the Bible say anything about war?
Does religion cause most wars?
What does the Bible say about civil disobedience?
What does it mean for Christians to be in the world but not of the world?
Christian ministry - What is it?
Truth about Everything Else