Sentence:  His dying command makes in incumbent on his followers to offer the “unspeakable gift” alike at the door of cottage and palace, forecastle and cabin. Mountain top and vale— plain and ocean are to be made to rejoice in the “glad tidings of great joy.” How the <WSD>dark-hearted</WSD> of earth need its light. 
Meaning of the word marked with <WSD> tags:  Unenlightened; ignorant of holy teachings.