Do we have blanket immunity from Satan’s invasion? No, that protection is conditional on our responsible participation in God’s plan for our protection. Dr. Unger writes: “The Holy Spirit indwelling the believer ungrieved by sin (Eph 4:30) and unquenched by disobedience (1 Thes 5:19) most certainly precludes invasion by a demon spirit. But who dares assert that a demon spirit will not invade the life of a believer in which the Holy Spirit has been grieved by serious and persistent sin and quenched by flagrant disobedience?”

Neil Anderson, The Bondage Breaker, p. 181