He uses them in an attempt to cause positive believers to enter into mental attitude sins, etc. The angelic conflict is not some far-fetched spiritual theory but an ever present reality in the believer's life. And just as physical war in the human realm is not pretty, spiritual warfare is just as messy. The believer needs to appropriate, on a daily basis, the knowledge that his existence does not revolve around his marriage and children, or job, etc., and making everything comfortable, but revolves around the spiritual war ensuing around him. Man is not here to have a nice, tidy, comfortable, and safe life.
All war presupposes human weakness, and seeks to exploit it.
If you are advancing spiritually you can count on opposition from the enemy. You can also count on undeserved suffering as a gift from your faithful Father. Against the enemy we need to stand firm, but in the face of undeserved suffering we need to take the offensive and forge forward, not allowing the pressure to distract us from our final objective but to advance us along. Only major engagements involving all one's force lead to major successes and only great victories pave the way for great results. Wherever a great and positive goal exists a great battle is not only the most natural but also the best means of attaining it.