He was in an old-fashioned sense my favourite author because he could narrate the world so that you could understand it. It was a limited world, Updikeland inhabited by the American middleclass, people much alike among each other. But it was a world into which you happily stepped in with every new book and to which you became easily familiar.
Despite of its peculiarity and limitations, this world was closely related with my own world, similar to Tolstoy's world with its aristocratic houses standing high above but being inhabited with people like me.
Updike was very explicit and detailed in sexual things. If I ever had met him I would first of all have asked him, why. But I imagine that he would have told me about the old tradition of the Realists, to whom he and Balzac, Flaubert, Dickens, Tolstoy, Fontane and Thomas Mann belonged. All of them were very much concerned about their credibility and all were working hard to be accepted as trustworthy by the reader. The credit would often depend on whether the furniture in the living room was correctly described before the hero of the novel would enter.
So Updike used the events in the bedroom instead of the furniture in the living room and proved his correctness to the reader through his detailed knowledge. At least this is my theory.
By the way, there was nothing like the Tragedies of the bedroom, which Tolstoy, suffering a lot in this respect assumed behind all the tragedies of mankind. Updike reports a lot of sins, but most of the time there is amazingly even more grace, so that sin must not necessarily cause tragedy. This has certainly to do with Updike’s lifelong confession that he was a Christian.
As a young man he found a simple formula* for his faith:
1. If God does not exist, the world is a horror-show.
2. The world is not a horror-show.
3. Therefore, God exists.
This may not suffice to build a dogmatic structure upon, but you can try this rule of three occasionally as a household remedy in case the existence of God will appear questionable. 
Whether this approach is sufficient to get into heaven is a different question. Everybody wishes for John Updike that he was well received up yonder after his death on January 27, 2009.
According to Catholic understanding, the Protestant Updike could have taken advantage of his second wife's testimony. She said about the man who smiles friendly on most of the photos, that he is the most good-hearted man in the world.
This is how I want him to remember.
* quoted from his autobiography, "Self-Consciousness" of 1989, published by Knopf, page 230
