Quoting John MacArthur from his book The Truth War (pages 25-26):
The gospel message in all its component facts is a clear, definitive, confident, authoritative proclamation that Jesus is Lord, and that He gives eternal and abundant life to all who believe. We who truly know Christ and have received that gift of eternal life have also received from Him a clear, definitive commission to deliver the gospel message boldly as His ambassadors. If we are likewise not clear and distinct in our proclamation of the message, we are not being good ambassadors.
But we are not merely ambassadors. We are simultaneously soldiers, commissioned to wage war for the defense and dissemination of the truth in the face of countless onslaughts against it. We are AMBASSADORS – with a message of good news for people who walk in a land of darkness and dwell in the land of the shadow of death (Isaiah 9:2). And we are SOLDIERS – charged with pulling down ideological strongholds and casting down the lies and deception spawned by the forces of evil (2 Corinthians 10:3-5; 2 Timothy 2:3-4).
Notice carefully: our task as ambassadors is to bring good news to people. Our mission as soldiers is to OVERTHROW FALSE IDEAS. We must keep those objectives straight; we are not entitled to wage physical warfare against people or enter into diplomatic relations with anti-Christian ideas. Our warfare is not against flesh and blood (Ephesians 6:12); and our duty as ambassadors does not permit us to compromise or align ourselves with any kind of human philosophies, religious deceit, or any other kind of falsehood (Colossians 2:8).
If those sound like difficult assignments to keep in balance and maintain in proper perspective, it is because they are indeed. Jude certainly understood this. The Holy Spirit inspired him to write his short epistle to people who were struggling with some of these very same issues. He nevertheless urged them to contend earnestly for the faith against all falsehood, while doing everything possible to deliver souls from destruction: “pulling them out of the fire, hating even the garment defiled by the flesh” (Jude 23).
So we are ambassador-soldiers, reaching out to sinners with the truth even as we make every effort to destroy the lies and other forms of evil that hold them in deadly bondage. That is a perfect summary of every Christian’s duty in The Truth War.