What does the speaker say farewell to in the poem?

Read the following passage and answer the questions by choosing the correct option :-

The sun descending in the west,
The evening star does shine;
The birds are silent in their nest.
And I must seek for mine

The moon, like a flower
In heaven's high bower
With silent delight
Sits and smiles on the night

Farewell, green fields and happy grove,
Where flocks have took delight:
Where lambs have nibbled, silent move
The feet of angels bright;

Unseen they pour blessing
And joy without ceasing
On each bud and blossom,
And each sleeping bosom.

They look in every thoughtless nest
Where birds are covered warm:
They visit caves of every beast,
To keep them all from harm:

If they see any weeping
That should have been sleeping
They pour sleep on their head,
And sit down by their bed