The theme is the difference between having a girlfriend and her being your wife. And from that simple premise, he weaves wonderful tales and insights that has the audience roaring. In fact, his opening, simple description of the difference lasts almost 15 minutes. Yet it's all insightful and builds upon that starting comic foundation to an even larger point. And that point itself grows for 45 minutes. Only at that point does he get into the concept of children. And though brief by comparison, that's wonderful, as well -- and ties in with having a wife, too.
Cosby makes very clear that in all his blunt observations he's not being critical of having a wife, just noting the difference. As he says, when a man answers a question by saying that "My wife is my best friend," it's not true. But in saying it's not true, Cosby emphasizes that a wife is on a much higher plane than a mere friend. But the husband still has to say she's your best friend, at the risk of being killed.
He also makes clear that much as men think that as The Man of the House they have responsibility, they actually have none.
The thing that was perhaps most fun for me is that it harkened back several years ago when a good friend got married, and his wife's father was a major mucky-muck agent. And later in the evening at the wedding, Bill Cosby (one of his clients) showed up after having hosted the Playboy Jazz Festival at the Hollywood Bowl. He delivered a hysterical speech to the newly-married couple that in many ways was a precursor to this TV special. It was about the responsibilities the new groom had to grasp. "Starting from now on," he said, "you must understand that when your wife says 'Good night' and that she's going up to bed...whatever you are doing is over, and you are going up to bed, as well. It may sound like she is only the one going to bed, but no, you both are."
No, according to Bill Cosby, a marriage is the wife's world, and the husband is there to go along for the ride.