Paul urges us to put on the whole armour of God, not part of it or half of it. It reminds me of the story in Greek mythology of Achilles who was predicted a young death. So his mother dipped him in the River Styx which was supposed o have magical properties. Where his other held him by his heel he was not protected and later died by a poisoned arrow piecing that part of his foot.
Our armour against the whiles of the devil needs to be complete; we never know where he will attack us next. We need to have the belt of truth round our waist and the breastplate of righteousness in place. In our hands we need the shield of faith and sword of the spirit, on our head the helmet of salvation.
We know that warriors of old needed complete armour protection. Any piece missing would result in death. Our battle against the power of darkness is no less important. Every piece of God’s armour is vital.