"The Wise Rabbi (adult themes may be offensive to relious)" joke

The madam of a bawdy house answered the ring of the bell and, on opening the door, she found standing there on the threshold, an ancient, bearded gentleman in rabbi's garb.
"May I come in?" asked the rabbi gently in an aged, quavering voice. Feeling a little confused, the madam said, "But rabbi, surely you must be in the wrong place. Here is where we..."
"I know what you do here," interrupted the rabbi. "You don't think I came here for chopped liver, do you? Bring on the girls."
Still confused, but understanding her professional duties, the madam had several girls line up. The rabbi tottered from one to another until he reached Rose, a large redhead with enormous breasts. He looked at her with appreciation and pointed, "Good! I'll take those."
The rabbi paid out the necessary sum and Rosie led him upstairs. She helped him off with his coat and hung it up carefully on the nail on the door.
Then she helped him off with the rest of his clothes and got into bed. There, to Rosie's astonishment, the rabbi performed with an address and a skill that was unbelievable. In fact, Rosie, a hardened professional, found herself surprised into orgasm. As they lay in bed a few minutes afterwards, relaxing, Rosie said, "How old are you, Rabbi?"
The rabbi said, "God has been good to me. I am eighty-eight years old."
"That is certainly amazing. Listen, Rabbi, if you're ever in the neighborhood again and if you should feel in the mood, please ask for me - Rosie. I would be delighted to oblige you."
The rabbi said, with a certain hauteur, "What do you mean, if I should be in the mood again? Let me sleep for five minutes right now and, believe me, I will be in the mood again."
"Really, Rabbi? Then please take a nap."
"Okay." The rabbi adjusted himself into a relaxed position, face up, placed his arms across his chest and then said, "Wait one minute. This is important. While I'm asleep, scoop up my testicles with your right hand and hold them an inch above the sheet, without moving them. Keep them absolutely motionless."
Of course, Rabbi," said Rosie, and did as she was told, holding the rabbi's testicles free of the sheet. For five minutes the rabbi slept, then woke with a start and said, "I'm ready."
And so he was, for, to Rosie's delight, he was even better the second time than the first. As she lay panting, Rosie said, "It was wonderful, Rabbi, but one thing I don't understand. Why was it necessary to hold your testicles motionless above the sheet while you were sleeping?"
"Oh that," said the rabbi. "Well, you are a nice girl and I like you very much. Still, the truth is I don't know you very well, and over there, in my coat, hanging on the hook on the door, is five hundred dollars."