Darwin lived a long life and his views changed during his life. He began as a conventional Christian, and ended it either agnostic or believing in a God, but only as First Mover. So it's possible to quote differing views from different stages of his life.
Darwin was very devoted to his wife who was a strong Christian. When he set out on his literal voyage of discovery on the Beagle he saw the wonders of nature as confirming the existence of a creative God. In time, his studies led him to a different conclusion. As a naturalist, he began to see the cruelties of nature as incompatible with his religion. Even tiny things in Nature shocked him. It was the fate of a breed of caterpillar, to serve as living food for its predator, that helped to tip the balance:
"I had no intention to write atheistically. But I own that I cannot see, as plainly as others do, & as I [should] wish to do, evidence of design & beneficence on all sides of us. There seems to me too much misery in the world. I cannot persuade myself that a beneficent & omnipotent God would have designedly created the Ichneumonidæ with the express intention of their feeding within the living bodies of caterpillars, or that a cat should play with mice."
Despite this, out of sensitivity for his wife's feelings, he recognised the implications of evolution for conventional Christianity and delayed publication of the Origin for the best part of two decades, until a rival drove him to commit to print. Even then, he was very reluctant to make any explicit connection with religion:
"...it appears to me (whether rightly or wrongly) that direct arguments against Christianity & theism produce hardly any effect on the public; & freedom of thought is best promoted by the gradual illumination of men’s minds, which follows from the advance of science. It has, therefore, been always my object to avoid writing on religion, & I have confined myself to science. I may, however, have been unduly biased by the pain which it would give some members of my family, if I aided in any way direct attacks on religion."
Darwin was a devoted family man, sensitive to offending religious sensibilities, and ultimately a reluctant sceptic. He is most unfairly characterised in some quarters today as some kind of devil in human form. I could only wish that more men today were as fine as Darwin.
Sometimes I wonder if Darwin's name gets confused with Dawkins, who writes today about evolution and who is indeed very outspoken against religion.