Lutheran theology affirms the legitimacy of military service through the doctrine of the two kingdoms and the theology of vocation. The two-kingdoms doctrine distinguishes between God's rule in the civil realm (through law, government, and coercion for the sake of order and justice) and his rule in the spiritual realm (through the Gospel). A Christian may serve as a soldier, judge, or magistrate in the civil realm as a legitimate expression of neighbor-love, since such service protects the innocent from harm.

Luther wrote extensively on this topic in 'Whether Soldiers, Too, Can Be Saved' (1526), affirming that soldiers who fight in just wars are fulfilling a godly vocation. Lutheranism endorses the classical just war criteria and is not a pacifist tradition. Voluntary conscientious objection is regarded as a personal moral decision that may be respected, but pacifism is not presented as a requirement of the Gospel. This distinguishes Lutheranism from Anabaptist traditions.