Genius is a neutral thing. It can be used for evil or good. In this case though mischief was apparently on his mind, something else clicked. Evil priests in the Old Testament sometimes were yet moved enough by the Lord to pass on a message that was definitely of the Holy Spirit.
From a speech by Leonard Cohen written 25 years before he wrote Hallelujah (from the above link)
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... And it involved telling stories. The story, Cohen knew, had kept the Jews alive. It captivated them even when the somber and accurate accounts of their progressions—thousands burned here, millions gassed there—were too much to bear. Canada, too, was surviving on account of a story: Its own chronology seared by divisions and stained by war, it told itself that it existed, that it was a real nation with a real unifying force, and, encouraged by that story, it persevered.
While all nations are, to some extent, imagined communities that come together only when all of their inhabitants envision them into being, Canadians and Jews had to imagine harder, hard enough to override history’s long odds. To create order, to make a community, to shape time, to find hope where logic and reason saw none: This is what the story accomplished. And it was the prophet’s job to tell the story.
Speaking to his fellow Montreal Jews, Leonard Cohen declared it his intention to tell the story as best as he could, not in pretty poems but in some other, new, unknown and throbbing way. To do it properly, he noted, he would have to go into exile. He would also have to stay stoic as his fellow Jews labeled him a traitor for daring to think up other possibilities for spiritual life—possibilities, like love and sex and drugs and song, for which there was little room in the synagogue. He was ready. As he finished his talk, the shouting began. His words about killing God, prophets as traitors, and the soulless rich enraged many in the audience. Some catcalled. Others demanded the time to debate. It was late at night, and the event’s organizers suggested that the discussion be continued the following Saturday night. Grumbling, irate, the audience scattered.
The following Saturday, the library was packed once again. On the dais, rabbis and community leaders sat gravely, ready to chastise Cohen for his impudence. But Cohen was no longer there. He was in his small white house in the Greek island of Hydra, playing his guitar outside his favorite taverna, dreaming up a new way to tell his stories, training to become a prophet.