The exact meaning of assimilate can depend upon its context. For example:
"assimilate to a new country" — fitting into a prevailing culture
"assimilate the information" — transform information within the mind into understanding
"assimilate the food" — transform nutrients within the body for its use
Or perhaps what it condoned was not the man's selfdedication to the saving of negro souls, but the public ignoring of the fact of that charity which they received from negro hands, since it is a happy faculty of the mind to slough that which conscience refuses to assimilate.
Chapter 15 (7% in)
There are no more uses of "assimilate" in Light in August.