Can anyone help me understand the Poem by Rupert Brooke "The Hill"?

The Hill - Rupert Brooke

Breathless, we flung us on the windy hill,
Laughed in the sun, and kissed the lovely grass.
You said "Through glory and ecstasy we pass;
Wind, sun, and earth remain, and birds sing still,
When we are old, are old...." "And when we die
All's over that is ours; and life burns on
Through other lovers, other lips" said I,
"Heart of my heart, our heaven is now, is won!"

"We are Earth's best, that learnt her lesson here.
Life is our cry. We have kept the faith!" we said;
"We shall go down with unreluctant tread
Rose-crowned into the darkness!".... Proud we were,
And laughed, that had such brave true things to say.
—And then you suddenly cried, and turned away.