The Gilgul of Park Avenue by Nathan Englander

Charles Luger receives a revelation one day while riding in a cab that he is Jewish. He simply decides that if he is Jewish he better begin living like a Jew. The bad news is that he decides to tell his wife after he has received this revelation. What makes it worse is that he decides to spring the news on her after she has been at a long day at work and has just finished the day with a root canal. She doesn't take the news well. So Charles decides to talk to someone who he believes can help: a Rabbi. Not just any Rabbi, but one that he simply finds looking in the phone book: Rabbi Meintz. The Rabbi helps Charles see less of the need to see his shrink and more to see the Rabbi. His wife gets even and invites the shrink to dinner where a full kosher meal will be served. He invites Rabbi Meintz. (You can imagine how it turns out) Charles eventually becomes a zealot fanatic of Jewish customs and laws to the point that he won't push elevator buttons on the Sabbath.

The Glass Cup of Elijah, Bohemian, 19th century.