Even if Darwin was religious,it's irrelevant to the issue and that was 150 years ago .before advances in biochemistry, physics , genetics ,math, chemical thermodynamics, non linear dynamics ,reaction kinetics etc. It takes knowledge of those and other subjects to understand evolution and it takes years to study those fields.
Check out the website talkorigins.com if you are seriously interested in evolution especially their "posts of the month"
As far as Darwin spending years studying birds in the Galapogos islands to write a book and make money ,give me a break.