Sentence:  In the old days, to my commonplace and unobserving mind, he gave no evidences of genius whatsoever. He never read me any of his manuscripts, ..., and <WSD>therefore</WSD> my lack of detection of his promise may in some degree be pardoned. 
Meaning of the word marked with <WSD> tags:  Consequently, by or in consequence of that or this cause; referring to something previously stated.