Kabbalah for Yoma 77:10

215. The agents of Sitra Achara have three functions. The first is to seduce man to sin through which he becomes impure, as stated in Gemara (Yoma), "When man acts impurely below, He is made impure from above." These forces from which the Yetzer Hara - Evil inclination stems, draw man toward sin by causing it to appear sweet and pleasant, as stated, "Sweet is stolen water". The Zohar refers to this as "The pleasure with impurities". None the less the purpose in their creation is to merit the righteous. Through conquering the evil inclination, which seems? insurmountable, the righteous are rewarded in direct proportion to their effort, as stated, "According to the difficulty is the reward". All this is explained at length in the Zohar through the allegory of the king who sent a harlot to seduce his son. He stipulated to her that if she succeeds all the goodness that would have rightly been given to his son would be hers instead. But, if he shunned her advances the prince would receive great reward and she too would be rewarded since through her great efforts he merited this goodness. Throughout, the fathers' intent was for the good of his son, and even the Harlot, though she appeared in the guise of a temptress, was the kings agent and secretly desired the princes success.