The Bible recognizes war as a somber reality of a fallen world, sometimes commanded by God in specific redemptive-historical contexts (such as the conquest of Canaan) and permitted for civil magistrates to maintain justice and defend the innocent under the New Testament. While Christians are called to be peacemakers, both Reformed and Particular Baptist traditions maintain that the use of force by the state in just and necessary circumstances is not inherently sinful.
The Reformed tradition, as expressed in the 1689 LBCF Ch.24 §2, holds that it is lawful for Christians to serve as magistrates and, in that capacity, to wage war upon just and necessary occasions to maintain justice and peace. This view is echoed in the Westminster Confession of Faith Ch.23 §2, which affirms the same necessity for the preservation of a commonwealth. The magistrate does not bear the sword in vain, as noted in the Second Helvetic Confession, which explains that the sword is to be drawn against malefactors and for the defense of the people. This is grounded in the biblical principle that the civil government is an institution ordained by God for the order of society.
In the Old Testament, Israel received specific instructions regarding the conduct of war. In Deuteronomy 20:1, the Lord instructed the people not to fear their enemies, for He was with them. Further, in Deuteronomy 20:4, the text declares, "for Jehovah your God is he that goeth with you, to fight for you against your enemies, to save you." These wars were often tied to the specific inheritance of the land and the judgment of nations that practiced great abominations. While the New Testament emphasizes the gospel of peace, the principle that the Lord grants authority to human governments to restrain evil remains, as seen in the broader witness of Scripture that the Lord is the ultimate Arbiter of justice.
While the state may exercise the sword, the Christian's hope is not in earthly power, but in the gospel of Jesus Christ. As Augustine noted in The City of God, those who wage war in obedience to God's law or a just commission are acting as agents of public justice, not as personal murderers. Ultimately, we look forward to the day when Christ returns, the Prince of Peace, to establish a kingdom where war is no more. Until then, we live in a world that is more sinful than we dared believe, yet we are sustained by the grace of Christ, who has already won the ultimate victory over sin, death, and the devil. Our obedience is not a means to acceptance, but a fruit of the peace we have already found in Christ.