On ' A Thing of Beauty '

Often students of CBSE Class XII fail to follow the process that makes a thing of beauty a joy forever . And, CBSE has often asked why a thing of beauty is a joy forever according to John Keats .
The answer is quite clear and interesting . Look at the lines closely :-
" A thing of beauty is a joy forever
Its loveliness increases , it will never
Pass into nothingness ; but will keep
A bower quiet for us , and a sleep
Full of sweet dreams ,and health ,and quiet breathing ."
Now, these are the opening lines of his poem 'Endymion: A Poetic Romance'.The story in the poem is of Greek origin in which Endymion ,a beautiful young shepherd and poet,gets a vision of Cynthia ,the Moon Goddess and his love unto her goes on increasing and he sets out for her quest . She appears ever more beautiful to her and her quest turns to be ever more joyful .
It is love that makes a thing of beauty a joy forever because if we love a thing it appears more beautiful to us .Beauty generates love and love generates beauty . Thus both keep on increasing and render an everlasting joy .
That's why Keats uses the word 'loveliness' in the second line . By 'loveliness' he means 'beauty generated by love '. And, how can an increasing thing pass into nothingness ? Only diminishing things can do so .
So is a thing of beauty a joy forever .