So there's this young and very devout, but somewhat naive, pastor who goes off and gets married one day. And a year goes by, and two, and three, and five, and still there's no kids. And one day his parents come to visit, and his dad takes him aside and sort of casually inquires whether there's going to be grandkids any time soon.
"Well, we're hoping," says the pastor, "but we haven't been blessed so far. But we're patient that God will provide."
"Is there some medical problem?" his dad asks. "I mean, the two of you don't have any problems when you, well, you know, do you?" The pastor looks scandalized.
"Dad!" he says. "That would be wrong! Lust is a deadly sin! Judith and I have been living together for six years now. We just need to continue to be patient. If God wishes us to have children, he will provide!"
Dad rolls his eyes and says, "Listen, son, I admire your piety, but let me wise you up to a thing or two: There's a few things that you have to do for yourself, that God ain't gonna do for you. He gave you the equipment; your part of the deal is you gotta use it for what he intended it for."
"Dad," says the pastor, "you mean....?"
"Yup," says his dad. "Man cannot breed by life alone."