Power belongs to God alone. It does not belong to evil, not ever. And when you and I are convinced of this unchangeable fact, we are able to resist aggressive mental interference, which would otherwise temporarily obscure our responsibility as followers of Christ Jesus to destroy the supposed activity of evil.
It's important to know what we are defending ourselves against. For example, do we ever feel mentally burdened and wonder why? Do we sometimes wrestle with feelings of confusion or with a sense of "Oh, what's the use of trying"; with bad temper, self-absorption, fear—for no apparent reason? In whatever form intrusive suggestions come to us, they cause us to feel cut off from God's love and support. They lead us to think and behave in a manner contrary to God's commands and direction. What's worse, they may argue that we don't care. This we can't afford to let happen.
Mary Baker Eddy points out, "The whole world needs to know that the milder forms of animal magnetism and hypnotism are yielding to its aggressive features." She says further: "People may listen complacently to the suggestion of the inaudible falsehood, not knowing what is hurting them or that they are hurt. This mental bane could not bewilder, darken, or misguide consciousness, physically, morally, or spiritually, if the individual knew what was at work and his power over it." Then she says even more strongly: "The crimes committed under this new-old régime of necromancy or diabolism are not easily reckoned. At present its mystery protects it, but its hidden modus and flagrance will finally be known, and the laws of our land will handle its thefts, adulteries, and murders, and will pass sentence on the darkest and deepest of human crimes." Message to The Mother Church for 1901, pp. 19-20.