On 6th March 1860, Charles Darwin advised Samuel Pickworth Woodward, a naturalist and geologist he correctly believed to be sceptical of his views, on how to go about reading On the Origin of Species:
The fair way to view the argument of my book, I think, is to look at Natural Selection as a mere hypothesis (though rendered in some degree probable by the analogy of method of production of domestic races; & by what we know of the struggle for existence) & then to judge whether the mere hypothesis explains a large body of facts in Geographical Distribution, Geological Succession, & more especially in Classification, Homology, Embryology, Rudimentary Organs The hypothesis to me does seem to explain several independent large classes of facts; & this being so, I view the hypothesis as a theory having a high degree of probability of truth. All turns on whether the above classes of facts seem to you satisfactorily explained or not.
In other words, think of evolution by means of Natural Selection as an idea worthy of consideration, then actually consider the facts which can be explained by Darwin’s idea, and decide whether you find them compelling.
You can’t, within reason, ask more of a reader than that.
Unfortunately, in this case, Darwin’s correspondent found it impossible to accept Darwin’s views.