In it Darwin, referring to his Origin of Species: 1) admitted that his primary objective was not scientific but religious, i.e. anti-creation ("I had two distinct objects in view; firstly, to shew that species had not been separately created, and secondly, that natural selection had been the chief agent of change" - my emphasis); 2) retreated from his theory of natural selection by supplementing it with Lamarckian inheritance of acquired characteristics ("natural selection had been the chief agent of change, though largely aided by the inherited effects of habit, and slightly by the direct action of the surrounding conditions" - my emphasis); 3) effectively admitted that he had "extend[ed] too far the action of natural selection" and 4) had "exaggerated its power"; and 5) had given "to natural selection great power":
"I may be permitted to say, as some excuse, that I had two distinct objects in view; firstly, to shew that species had not been separately created, and secondly, that natural selection had been the chief agent of change, though largely aided by the inherited effects of habit, and slightly by the direct action of the surrounding conditions. I was not, however, able to annul the influence of my former belief, then almost universal, that each species had been purposely created; and this led to my tacit assumption that every detail of structure, excepting rudiments, was of some special, though unrecognised, service. Any one with this assumption in his mind would naturally extend too far the action of natural selection, either during past or present times. Some of those who admit the principle of evolution, but reject natural selection, seem to forget, when criticizing my book [The Origin of Species], that I had the above two objects in view; hence if I have erred in giving to natural selection great power, which I am very far from admitting, or in having exaggerated its power, which is in itself probable, I have at least, as I hope, done good service in aiding to overthrow the dogma of separate creations." (Darwin, C.R., "The Descent of Man and Selection in Relation to Sex," , John Murray: London, 1874, Second Edition, 1922, reprint, p.92).
Of these, the last admission is perhaps the most important, since it applies not just to Darwin, but to all Darwinists, namely, it is Darwinists who give to natural selection its power!
It reminds me of the prophet Isaiah's ridiculing of those who make an idol and then bow down to it, forgetting that it is they who gave to the idol any power it has over them:
Isaiah 44:15-17 "15 It is man's fuel for burning; some of it he takes and warms himself, he kindles a fire and bakes bread. But he also fashions a god and worships it; he makes an idol and bows down to it. 16Half of the wood he burns in the fire; over it he prepares his meal, he roasts his meat and eats his fill. He also warms himself and says, `Ah! I am warm; I see the fire.' 17From the rest he makes a god, his idol; he bows down to it and worships. He prays to it and says, `Save me; you are my god.'"
Indeed, Darwin actually called natural selection "my deity"!:
"MY DEAR GRAY ... I hope you have received long ago the third edition of the `Origin.' ... I have been led to think more on this subject of late, and grieve to say that I come to differ more from you. It is not that designed variation makes, as it seems to me, my deity `Natural Selection' superfluous, but rather from studying, lately, domestic variation, and seeing what an enormous field of undesigned variability there is ready for natural selection to appropriate for any purpose useful to each creature." (Darwin, C.R., Letter to Asa Gray, June 5, 1861, in Darwin, F., ed., "The Life and Letters of Charles Darwin," , Basic Books: New York NY, Vol. II., 1959, reprint, pp.165-166. My emphasis).