Spiritual warfare is the ongoing, supernatural battle in which the believer, empowered by the Holy Spirit, resists the persistent temptations of the devil, the world, and their own remaining corruption. It is not fought with worldly weapons, but by taking up the full armor of God to stand firm in the victory already secured by Jesus Christ.
Spiritual warfare is not a struggle against human enemies, but a reality inherent to the Christian life. As the Apostle Paul writes, Ephesians 6:12, "For our wrestling is not against flesh and blood, but against the principalities, against the powers, against the world-rulers of this darkness, against the spiritual [hosts] of wickedness in the heavenly [places]." We are called to "put on the whole armor of God" so that we may stand against the schemes of the enemy, resting in the finished work of Christ rather than our own strength (Ephesians 6:11).
A vital component of this warfare is the battle against indwelling sin. The 1689 LBCF Ch.13 §2 teaches that sanctification is imperfect in this life, leaving remnants of corruption that create a "continual and irreconcilable war." John Owen, in his classic treatise On the Mortification of Sin in Believers, emphasizes that mortification is not merely the suppression of sin but the constant reliance on the Spirit to keep it from dominating our lives. Because the regenerate part of the believer is strengthened by the "sanctifying Spirit of Christ," we are enabled to overcome and grow in grace (1689 LBCF Ch.13 §3).
The gospel is the A to Z of our warfare; we do not fight for victory, but from the victory of Christ. The saints "conquered him by the blood of the Lamb" (Revelation 12:11). Our primary weapon is the "sword of the Spirit, which is the word of God" (Ephesians 6:17), and our posture is one of constant prayer in the Spirit. As you feel the weight of your own flaws, remember that you are more accepted in Christ than you dared hope—and it is that very acceptance that empowers your resistance to sin.