In the poem Endymion: A poetic romance (1818), the first stanza of Book I (beginning, "A thing of beauty is a joy for ever") contains the following passage:-
yes, in spite of all,
Some shape of beauty moves away the pall
From our dark spirits. Such the sun, the moon,
Trees old, and young, sprouting a shady boon
For simple sheep; and such are daffodils
With the green world they live in; and clear rills
That for themselves a cooling covert make
'Gainst the hot season
I was told that "simple sheep" was a biblical reference (I presume it to be related to how we are all sheep following a Shepherd or something). However, I couldn’t find anything in particular related to it nor could I interpret what it could be as Keats was describing beauty till this point.