What is the central idea of the poem "God's Grandeur"?

The central idea of this poem is that the "grandeur of God" is so fundamentally a part of the world, which he created and "charged with" his power and beauty, that it can never entirely be "spent." It can appear, at times, that after generations of men have "trod" and "toiled" through the soil and earth God laid down, surely that beauty should have been trampled out of it—especially because some no longer "reck his rod," or think of God and his presence and capabilities.
However, according to the poet, it is not true that the beauty with which God imbued the earth can ever be "spent." On the contrary, his grandeur is represented in the continuing beauty put forth by nature; God is "deep down things." Even when it seems that the world is dark and the "last lights" have gone, God, embodied in the symbolic idea of morning and rebirth, is still here. The Holy Ghost "broods" like a mother over the "bent" world, enfolding it in his "bright wings." The imagery here seems to compare the Holy Ghost to a mother bird protecting its young, enfolding the earth and its inhabitants in the cradle of his wings and protecting us even when some doubt his continuing presence.