Answer:
Several meanings could be agvined to this. On face value, Dr. King is saying that the men who lynched Emmett Till were morally bankrupt but hid behind Christianity and rationalized their actions for murdering Emmett for allegedly flirting with a married white woman.
There is no key to civilization. The concept that native americans did not have a civilization or were not civilized is one only supported by the egotism and arrogance of the empirical profit oriented "conquerers" who have worked to eradicate all cultures that conflict with profits. The key to western civilization that allowed them to kill off the majority of the natives was a lack of respect for life and insane drive for control, ownership and dominance, to which the peaceful and sophisticated Natives would not stoop.
