Oh dear, what is the matter with your sense of humour today? To mexplain it would be rather crude. His wife is saying that he should pray for "stiffness", i.e, an erection and after that she will "guide" it, infering that they haven't had sex for a long, long time.
"You can be young without money but you can't be old without money"
Maggie the Cat from "Cat on a Hot Tin Roof." by Tennessee Williams