Spiritism reveals to us that we are imperfect souls on a quest to become pure spirits. What many considered bad spirits, demons, or manifestations of the devil are spirits who have not yet learned the true path to goodness. They are ignorant, immature, or rebellious spirits who reject the hard path to perfection required.
Allan Kardec’s, The Spirits Book, tells us the answer in Question 131. Are there any demons in the usual acceptation of that term?
“Men have done in regard to devils what they have done in regard to angels. Just as they have imagined that there are beings who were created perfect from all eternity, so they have imagined that spirits of the lower degrees were beings essentially and eternally bad. The words demon, devil, ought, therefore, to be understood as indicating impure spirits who are often no better that the imaginary beings designated by those names, but with this difference, namely, that their state of impurity and inferiority is only transitory. They are the imperfect spirits who rebel against the discipline of trial to which they are subjected, and who, therefore, have to undergo that discipline for a longer period, but who will, nevertheless, reach the goal in time, when they shall have made up their minds to do so. The words demon, devil, might accordingly be employed in this sense; but as they have come to be understood exclusively as conveying the meaning now shown to be false, their employment might lead into error by seeming to recognize the existence of beings specially created for evil.”
“As regards the term “Satan,” it is evidently a personification of the principle of evil under an allegorical form for it is impossible to admit the existence of a being who fights against God as an independent and rival power, and whose sole business in life is to contravene His designs. As images and figures are necessary in order to strike the human imagination, men have pictured to themselves the beings of the incorporeal world under a material form, with attributes indicative of their good or bad qualities. It is thus that the ancients, wishing to personify the idea of time, represented it under the figure of an old man with a scythe and an hour-glass. To have
personified it under the figure of a youth would have been contrary to common sense. The same may be said of the allegories of Fortune, Truth, etc. The moderns have represented the angels or pure spirits under the form of radiant beings with white Wings-emblem of purity Satan, with horns, claws, and the attributes of bestiality-emblems of the lowest Passions; and the vulgar, prone to understand such representations literally, have taken these allegorical embodiments of abstract ideas for real personalities, as they formerly did in regard to the allegorical personifications of the old mythology.”
Hence, what are considered evil spirits in many religions and superstitions are actually poor unfortunate souls who haven’t yet ascended. They are there to take advantage of people in their time of weakness or want. One day, with our help and help from the spirit world they shall learn that the path of love and kindness is superior to all others.