The final piece of defensive equipment is the helmet of salvation. This helmet protects our minds from attacks against the assurance of our salvation. Satan will accuse us of not doing enough for God and then will call into question the validity of our salvation. Understanding and applying the doctrine of salvation by grace alone is certainly one element of what it means to put on the helmet of salvation.
Remember
For by grace you have been saved through faith, and that not of yourselves; it is the gift of God, not of works, lest anyone should boast. Ephesians 2:8–9
Not by works of righteousness which we have done, but according to His mercy He saved us. Titus 3:5a
Hope of Salvation
There is, I believe, another aspect to the helmet of salvation. In writing to the Thessalonians, Paul exhorted them to put on as a helmet the hope of salvation (1 Thessalonians 5:8). I think that’s also the idea here in Ephesians. What that means practically for Christians is simply that a time is coming when we are going to be gloriously delivered from this present evil world and taken to Heaven! Our future hope is something Paul wanted us to keep at the forefront of our minds. No matter how tough it gets, there is an end in sight. One day the battle will be over and we’ll settle down forever with our great King and Savior in His unspeakably glorious kingdom. Remember that, and let that thought spur you on.