The conflict in this poem doesn't seem to me to be about the conflict between earthly and heavenly existence. I think the poem makes it fairly clear that the conflict is based on the way in which we are able to perceive the full glories of nature as a child, and that we gradually lose this ability as we grow older. This is what the final two stanzas of this poem refer to. The poem ends as the speaker of this Ode recognises and accepts the waning of his faculties in regards to being aware of the joys of nature and being open to learning of them, but with an insistence that he will still do his best to rejoice in the beauty of nature:
What though the radiance which was once so bright
Be now for ever taken from my sight,
Though nothing can bring back the hour
Of splendour in the grass, of glory in the flower;
We will grieve not, rather find
Strength in what remains behind...
Even though the same kind of visceral and intimate connection with nature, it is suggested, is now no longer possible, the speaker resolutely determines not to "grieve" in this loss. Instead, he will focus on what "remains behind" in terms of his ability to meditate upon the glories of nature. The poem ends then not in a tone of pessimism but in one of optimism as the speaker celebrates the strength of the human heart and recognises "man's mortality" in how aging necessarily involves a loss of perception of nature and of its beauty.
Thanks to the human heart by which we live,
Thanks to its tenderness, its joys, and fears,
To methe meanest flower that blows can give
Thoughts that do often lie to deep for tears.
Age necessarily involves diminished perception, but the speaker determines to use what faculties remain to him to continually rejoice in nature.