Symbolism of musical key in Bach music?

I am reading a couple of books about the symbolism in Bach's work, with some information on numerology, but does anyone know what each musical key represents? I seem to recall that D Major is the key of God? Any good websites about this topic?

The idea that various keys have symbolism is not unique to Bach. It is called the Doctrine of Affections, and was most popular as an idea during the Baroque era. D Major is associated with royalty and God, generally, yes. C Major is associated with light. There are various others.

This idea originated during a time when instruments were tuned with what is called unequal temperament. This means that an instrument, especially a keyboard, would not have an equal sonic distance between half-steps. This means that each key had a different aural "flavor". This doesn't really apply today, when instruments have equal temperament and most keys sound the same to people without perfect pitch.

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I think the symbolism of the keys, as well as anything to do with numerology, is a bunch of hogwash. So that solves your problem!

There is a lot written about numbers in Bach's work. The trouble with almost al kinds of studies is that they go way to far in my opinion. There might be examples of symbolism and some of them are quit obvious. Not all the examples are numeric, some are very different in nature. There is the "cross motive" where the melodic line has the shape of a cross.
There are numeric proportions in fugues etc.
D Major is indeed considered to be a royal key. This symbolism lasted even a bit longer.
Eb Major was a Heroic Key. Beethoven wrote his Eroica in Eb, Ein Heldenleben was written in Eb etc. It is however sometimes difficult to say if it is the actual Key that creates the symbolic. In the case of Ein Heldenleben, it seems to be Beethoven's Eroica that was the association with Heroism.