The poem reveals that cummings not only believes in God, but finds faith in the deity through the beauty of the incarnate world, which cummings joyously celebrates in these verses. In other words, cummings believes in God because he can experience the world with his five senses and find it good.

cummings thanks God for the:

leaping greenly spirits of trees
and a blue true dream of sky; and for everything
which is natural 

The poem thus illustrates that the poet is filled with gratitude for the natural world and for the God he believes created it. The poet embraces the infinite, which he calls "yes," and finds not sin and despair but hope and happiness in the world around him. The poem shows that cummings had at least moments of profound optimism, moments when he felt fully alive to the world, when "the ears of my ears awake," and the eyes of his eyes open. He wonders how anyone who could experience the earth with his senses -- "tasting touching hearing seeing" -- could doubt the existence of God. 

The first thing that it appears to reveal about cummings is that he believes in God.  He addresses the poem to Him, as a sort of oblation, a prayer of gratitude. He even opens up in the style of a prayer by saying "i thank You God for most this amazing day."  So, he believes in God, and given the text of the poem, is grateful that God made such a beautiful day, a beautiful earth to live in.

Note also cummings' unusual use of capitalization when speaking of God.  Cummings is famous for never capitalizing anything at all.  He messes with the rules of standard spelling and punctuation a lot, and even in his own name he didn't capitalize.  It is e.e. cummings, not E.E. Cummings.  So, the fact that he deviates from his non-capitalization in order to write "God," shows the deep respect and reverence that he must have for God.  He refers to God as You, with a capital Y also.  Capitalizing indicates honoring someone that you respect and admire, and showing your deference for them.

In addition to his belief and reverence for God, we can tell that cummings enjoys nature and the beautiful things of the earth.  It invigorates and enlivens him.  The entire poem is a rejoicing of the beauty that can be found in God's nature.

I hope that those thoughts helped; good luck!