As a soldier puts on his armor, there are some pieces that are put on last (kind of like a football player putting on his protective gear). But the order does not set the value, as a soldier’s helmet is absolutely essential to protect his head and his mind, which controls everything that he does and the choices that he makes. This is the place the enemy seeks to infiltrate and control.
For the Christian, his helmet (which protects his mind, his decisions, his actions, etc.) is his salvation. The knowledge and confidence that one (1) has been saved from his past sins by the blood of Christ and is now a “new creature” (2 Cor. 5:17), and (2) continues to be saved by the blood of Christ (1 John 1:7), and (3) will ultimately be saved eternally when Christ returns (1 John 5:13) truly is the helmet that protects one’s mind! Thus, Paul identified the helmet as “the hope of salvation” (1 Thess. 5:8).
When we battle with our adversary, we can hold our heads/helmets high that Christ gives us victory through His salvation of our sins! – DS