It's important for us to understand those forces, and for us to be on the lookout for them. And we have to realize that we aren't strong enough, all by ourselves, to hold on against some of these forces. That's a really important point. Nobody is strong enough to deal with some of the things that all of us have to face. And I don't just mean outward, physical things.
Nobody can outrun a bullet.
Nobody can stop a tornado. But nobody is strong enough, all by themselves, to handle all of the thoughts, all of the feelings, or all of the forces of evil that are around us and inside of us. We need to have help, and we need to have protection. We need to have invisible armor. The examples that Paul gives are pretty simple.