Is it permissible for a Christian to serve in the military?
A Christian may engage in any walk of life or profession so long as the work itself doesn't violate the believer's conscience or convictions nor run counter to God's word. In this case, the Bible never prohibits a Christian from serving in the military, and we even find examples of Christians serving as soldiers during the first century church in the book of Acts (see Acts 10).
Some have suggested that Christians cannot serve in the military because they might be required to engage in war-time activities, especially shooting and killing enemy soldiers. This is a wrong assumption without foundation in Scripture. The Bible distinguishes between unlawful killing and lawful killing. The Bible prohibits murder, which is the unlawful taking of a human life, but the Bible permits lawful killing as in war or when carrying out capital punishment under the authority of the state. The right to take a human life lawfully was given by God in Genesis 9.
Personally, if you feel convicted by the Spirit not to serve in the military, then you should listen to the Spirit and refrain from military service. On the other hand, if your government requires you serve in the military, then Paul tells us in Romans 13 we should submit to the government authorities.