Earth hath not anything to show more fair:
Dull would he be of soul who could pass by
A sight so touching in its majesty:
This City now doth, like a garment, wear
The beauty of the morning; silent, bare,
Ships, towers, domes, theatres and temples lie
Open unto the fields, and to the sky;
All bright and glittering in the smokeless air.
Never did sun more beautifully steep
In his first splendor, valley, rock, or hill;
Ne'er saw I, never felt, a calm so deep!
The river glideth at his own sweet will:
Dear God! The very houses seem asleep;
And all that mighty heart is lying still!
These lines acknowledge that although the scene he sets is completely devoid of human life, there is a “mighty heart” that lies in wait underneath, ready to spring to life. 
 ‘Dear God’ is exclamatory, address to a higher Power, expressing the poet’s overwhelming emotion. 
 The ‘houses seem asleep’ is an example of  metonomy  where the houses represent the people living within them. 
 The last four words could be considered a paradox because a living heart does not lie still but is always beating. Wordsworth is referring to the heart of the city which exits in the people and infrastructure. The  personification  of a non-existent mighty heart of the city lying still is the paradox. 
 There is also a possible interpretation of “lying still” meaning ‘still telling a falsehood’, that of the terrible reality of London poverty and squalor, compared to the romantic, imaginative,poetic vision.
Composed upon Westminster Bridge September 3 1802