Darwin’s religious thinking

Dear Sir
It seems to me absurd to doubt that a man may be an ardent Theist & an evolutionist. […] What my own views may be is a question of no consequence to anyone except myself.— But as you ask, I may state that my judgment often fluctuates. Moreover whether a man deserves to be called a theist depends on the definition of the term: which is much too large a subject for a note. In my most extreme fluctuations I have never been an atheist in the sense of denying the existence of a God.— I think that generally (& more and more so as I grow older) but not always, that an agnostic would be the most correct description of my state of mind.
Yours faithfully.
Ch. Darwin