We should not spar with demons. We should make outright war on them.
A similar call to arms is, of course, issued by Paul in Ephesians 6. Christians are called to a total war with the spiritual forces of evil, as we should be. After all, it isn't as though evil is interested in a friendly tussle with us. Evil is out for our total destruction, and it is armed for the task.
Amid all our efforts to please God, three pitfalls lie, prepared for us by demons. First is their attempt to impede any sort of worthwhile achievement; and if this fails they strive secondly to ensure that what we do should not be in accordance with the will of God. And if the scoundrels fail in this too, then they stand quietly before our soul and praise us for the fact that in every respect we are living as God would wish.
That is a shockingly comprehensive list of the ways humanity can be tempted to sin. Either we can do nothing at all, we can do things which conflict with the will of God, or we can glory in whatever good we accomplish.
In response, John suggests two paths to avoid falling into temptation. The first is vigilance.
The man who has conquered the passions has injured the demons, and by pretending to be still subject to them he deceives his enemies and remains invulnerable to them.
The second is fear of God.
We should be afraid of God in the way that we fear wild beasts. I have seen men go out to plunder, having no fear of God but being brought up short somewhere at the sound of dogs, an effect that the fear of God could not achieve in them.