Yoghurt On A Grecian Urn

Those, who can thus express a flowery
 tale more sweetly than our rhyme

What I think will be the final Keats poem for now is 'Ode on a Grecian Urn'. I am covering this because when I used the following lines:

Heard melodies are sweet, but those unheard
Are sweeter; therefore, ye soft, pipes, play on;

The lines are a more poetic version of 'the grass is always greener on the other side.' Of course, my inability to learn poetry restricts the efficacy of the quote as I inevitably butcher it. I will keep it short and only provide the first two verses.

THOU still unravish'd bride of quietness,
Thou foster-child of Silence and slow Time,
Sylvan historian, who canst thus express
A flowery tale more sweetly than our rhyme:
What leaf-fringed legend haunts about thy shape	5
Of deities or mortals, or of both,
In Tempe or the dales of Arcady?
What men or gods are these? What maidens loth?
What mad pursuit? What struggle to escape?
What pipes and timbrels? What wild ecstasy?	10
Heard melodies are sweet, but those unheard
Are sweeter; therefore, ye soft pipes, play on;
Not to the sensual ear, but, more endear'd,
Pipe to the spirit ditties of no tone:
Fair youth, beneath the trees, thou canst not leave	15
Thy song, nor ever can those trees be bare;
Bold Lover, never, never canst thou kiss,
Though winning near the goal—yet, do not grieve;
She cannot fade, though thou hast not thy bliss,
For ever wilt thou love, and she be fair!