Mad Song
by William Blake
The wild winds weep,
And the night is a-cold;
Come hither, Sleep,
And my griefs infold:
But lo! the morning peeps
Over the eastern steeps,
And the rustling birds of dawn
The earth do scorn.
Lo! to the vault
Of paved heaven,
With sorrow fraught
My notes are driven:
Lo draws attention to an interesting event. 
 In this case, it is drawing attention to the sky which is being lit by the rising sun. Despite the positive words being used, such as heaven, the speaker cries out with sorrow. The vault brings to mind a vaulted ceiling such as would be seen in a Cathedral. 

Mad Song