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Read "Sonnet" by James Weldon Johnson

My heart be brave, and do not falter so,
Nor utter more that deep, despairing wail.
Thy way is very dark and drear I know,
But do not let thy strength and courage fail;
For certain as the raven-winged night
Is followed by the bright and blushing morn,
Thy coming morrow will be clear and bright;
'Tis darkest when the night is furthest worn.
Look up, and out, beyond, surrounding clouds,
And do not in thine own gross darkness grope,
Rise up, and casting off thy hind'ring shrouds,
Cling thou to this, and ever inspiring hope:
Tho' thick the battle and tho' fierce the fight,
There is a power making for the right.

In which line does this sonnet's shift in tone, idea, or emotion occur?

"The way is very dark and drear I know,"
"Look up, and out, beyond, surrounding clouds,"
"There is a power making for the right."
"'Tis darkest when the night is furthest worn."