Verse 12 is a statement I think we often mentally mislay:
For our struggle is not against enemies of blood and flesh, but against the rulers, against the authorities, against the cosmic powers of this present darkness, against the spiritual forces of evil in the heavenly places.
So often our focus is on (real or perceived) “enemies of blood and flesh”, and I’m sure we can make our own list of these. And because we focus our attention on human “enemies”, we then forget, or misunderstand, what Paul says about how we are to engage in “our struggle”. We turn the struggle into something that is principally concerned with what we do or refrain from doing, whether that is by campaigning, writing blog posts, voting in church meetings (or political elections) and so on. In other words, law.
In contrast, just as Paul shows us our enemy is not who we think it is, so he shows us a different way in which to tackle this enemy:
Therefore take up the whole armour of God, so that you may be able to withstand on that evil day, and having done everything, to stand firm. Stand therefore, and fasten the belt of truth around your waist, and put on the breastplate of righteousness. As shoes for your feet put on whatever will make you ready to proclaim the gospel of peace. With all of these, take the shield of faith, with which you will be able to quench all the flaming arrows of the evil one. Take the helmet of salvation, and the sword of the Spirit, which is the word of God.
Now, the various parts of the “whole armour of God” (highlighted in bold) can often be seen as separate, and indeed some of them can often be given something of a “law” emphasis: living a righteous life, sharing the gospel, maintaining faith in God.
But it seems to me that these verses should not been understood as law, but as gospel. The whole armour of God is not a ragbag of different tasks assigned to us, but the single gospel of Christ in its different functions: as the “belt of truth”, as the gift of righteousness which is our breastplate, as the message whose proclamation overthrows the devil, as the salvation which protects us, and as the sword by which God defeats his (non-“blood and flesh”) enemies.
Seeing these verses as being solely concerned with the gospel and its work in and through us also saves us from “over-interpreting” them by minute examination of each metaphor. These verses are best taken as poetry, whose metaphors work upon us in their own right, rather than it being necessary for each image’s “objective”, didactic meaning to be unpacked before we can “really” understand this passage. I think it was Alan Bennett who said (to paraphrase, poorly) that if we can interpret a poem fully in prose, then it wasn’t really poetry to begin with.