The story Baring-Gould recounts may make one wonder why a witch would turn a wedding party into wolves. What is in it for her? The following passage of
Popular Tales from the Norse, by Sir George Webbe Dasent, explains:
One characteristic of all these witch trials, is the fact, that in spite of their unholy connection and intrigues with the Evil One, no witch ever attained to wealth and station by the aid of the Prince of Darkness. The pleasure to do ill, is all the pleasure they feel. This fact alone might have opened the eyes of their persecutors, for if the Devil had the worldly power which they represented him to have, he might at least have raised some of his votaries to temporal rank, and to the pomps and the vanities of this world. An old German proverb expresses this notorious fact, by saying, that 'every seven years, a witch is three halfpence richer'; and so with all the unholy means of Hell at their command, they dragged out their lives, along with their black cats, in poverty and wretchedness.
So it seems that just as "virtue is its own reward" then so too is evil, but why, after three years, does the witch in the story change the wolves back into human beings?