> The story is told by Felix Klein in the _Lectures on the
> Development of Mathematics in the 19th Century_, and his language
> sounds as though he had personal knowledge of it:
>
> The unusual nature of [Hilbert's] work produced quite diverse
> reactions. I resolved to draw Hilbert to Goettingen at the
> first opportunity. Gordan at first reacted negatively, saying
> "This is not mathematics, it is theology." But later he said
> "I have become persuaded that even theology has its uses." In
> fact, he himself substantially simplified Hilbert's argument.
This (1926) is the earliest negative interpretation of the quote, so
far as I know. Max Noether's 1914 version is pretty neutral.
Klein interpreted Gordan more sympathetically when the events
occurred, see Klein's correspondence with Hilbert in 1890-1893. In the 1926
passage clearly the story has become a "founding legend" of Klein and
Hilbert's Goettingen school.
The quote itself is not in the Klein-Hilbert correspondence, where
Gordan's reaction to the proof is discussed several times. I suspect the
Goettingen mathematicians learned it from Max Noether, who of course was
close friends with Gordan.
Colin