I rhyme / To see myself, to set the ... echoing (Seamus Heaney) (8)
I believe the answer is:
darkness
(Other definitions for darkness that I've seen before include "mystery" , "Better to light a candle than to curse it, they say" , "Gloom" , "'... cannot drive out ...: only light can do that'' (Martin Luther King)" , "Unlit state" .)