Reading Pamela Etter Mack via OnePotMeal leads me to 'God is in the details', as opposed to 'the Devil is in the details'. This takes me to Podhaka via Google. Her last comment there is interesting:

Bartlett's Familiar Quotations says

""God is in the details': A popular aphorism with the architect Ludwig Mies van der Rohe and the art historian Aby Warburg; attributed [Le bon Dieu est dan le detail] to Gustave Flaubert but without verification."

William Safire mentioned it in a New York Times article on July 30, 1989. He spoke with the editor of Bartlett's, who said:

"We've had little success with 'God (or 'the Devil') is in the details,'" says Mr. Kaplan. "We know that Mies van der Rohe used it in discussing architecture; Flaubert has been suggested, but nobody can find it in his writings. I think it may come from John Ruskin, because it sounds like him on the subject of workmanship, but we need the specific citation."