What does Emerson mean by It is a deliverance which does not deliver In the attempt his genius deserts him?

Emerson is expressing the idea that profound insights or truths can be experienced or understood, but cannot be fully articulated or shared through language. When trying to convey these profound insights, one's creative expression may fall short, unable to fully capture or communicate the depth of the experience. This can lead to a feeling of inadequacy or frustration in trying to convey something beyond the limits of human expression.