The poem
There is one sin: to call a green leaf gray, Whereat the sun in heaven shuddereth. There is one blasphemy: for death to pray, For God alone knoweth the praise of death.
There is one creed: ''neath no world-terror's wing Apples forget to grow on apple-trees. There is one thing is needful everything The rest is vanity of vanities.
St Francis of Assisi also wrote in praise of death, in his Canticle of the Creatures, otherwise knows as the Canticle of Brother Sun and Sister Moon. About two years before his death, he added to the Canticle a stanza in praise of "Sister Death".
But ...
... how can you say this poem is in praise of death? It's actually knocking calling time of death prematurely. THE most offensive thing one can do is call a green leaf gray; that is, say something's done for when it still has life in it. Recant, you heretic!