Theological half-gainers

In Christopher Buckley's unexpectedly caustic memoir about losing his parents, Patricia Taylor Buckley and William F. Buckley, Jr., he recounts his father's regret that a beloved friend whose ashes he and Christopher have just scattered was not a Catholic. "What do you mean, Pup?" Christopher asked.

He replied matter-of-factly that as Harry was not a Catholic, he had no expectation of seeing him again in heaven. This truly hit me like a smack in the face. Pup loved Harry wholeheartedly, but rules were—apparently—rules: The gates of heaven were shut against nonbelievers. I was crushed, for I too had loved Harry. I was, at the time (age twenty-eight), very much a believer, and I tended to take Pup's theological pronouncements as having ex cathedra papal authority.
    Sometime later, he spoke—with genuine relief in his voice—of his discovery of a loophole called "the doctrine of invincible ignorance," which, if I understand it—theological half-gainers can leave a lad's head spinning at times—means that the normal rules with respect to admission to heaven are suspended if you are incapable intellectually or culturally of accepting that the Catholic Church is the one true Church, the only means of redemption. How Pup smiled with relief as he explained it across the lunch table that summer day! –pp. 39-40, Losing Mum and Pup, Twelve, New York & Boston, 2009

Theological half-gainers! I wish I'd thought of that for my "definition of theology." Having only a vague sense that a "half-gainer" is some sort of dive, I looked it up (in yourdictionary.com):

gain·er (gnr): n. 2. Sports A dive in which the diver leaves the board facing forward, does a back somersault, and enters the water feet first.
half gainer: a fancy dive in which the diver springs from the board facing forward and does a back flip in the air so as to enter the water head first, facing the board.

What's fancy about a theological half-gainer is the believer's adroitness in positioning his head. Buckley is astute in classifying such theology a sport.