For we wrestle not against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickedness in high places (Ephesians 6:12).
In the armor of the Christian soldier, none is as indispensable as the helmet of salvation (v.17). Many soldiers have fought on after grievous and ultimately fatal wounds to their bodies. But a blow to the head (the mind) renders one either insensible, unconscious, or dead.
King David often described salvation in terms of military protection as he did in his great song of praise written to commemorate the defeat of Saul (II Samuel 22). It is a horn (mountain peak) from which to gain advantage over the enemy (v.3), and a shield (protective line of troops) behind which we are safe (v.36). It is also a rock (natural fortress) from which one can safely attack (v.47), and a tower, a place so safe that it inspires boasting (v.51).
Not only does this helmet protect us from the most damaging blows of the enemy, but it inspires us and emboldens us with confidence to take part in the battle. No soldier would ever fight without his helmet.
Yet many religious leaders today encourage us to put on a helmet of works of righteousness which we have done (Titus 3:5), or to protect our minds with philosophy and the tradition [teaching] of men, or the rudiments [logical systems] of the world (Colossians 2:8), rather than to place our faith in the risen Christ by embracing the grace of Gods salvation. We become wise unto salvation through a study of the Scriptures (II Timothy 3:15) and thereby become able to work out (our) own salvation (Philippians 2:12) as the gospel, which is the power of God unto salvation (Romans 1:16), makes it possible for God to work in us both to will and to do of His good pleasure (Philippians 2:13). HMM III