I've always read Hopkins's "Spring and Fall" as a sneakily sadistic little poem, its beautiful music pulsating against the psychological cruelty it dramatizes.
Margaret, are you grieving
Over Goldengrove unleaving?
An adult and presumably male speaker addresses his question to a "young child," importantly female. To begin with a question is to signal the speaker's ignorance, the gulf of unknowing that separates him from the mind of Margaret. He does not know the cause of her grief, but even as he states the question that reveals his ignorance, he projects a childish sentimentality upon the consciousness that remains a blank to him.
Leaves, like the things of man, you
With your fresh thoughts care for, can you?
Although still questioning, still uncertain, the speaker is now bold enough to force his own simile and metaphor upon the child he addresses. It is in his mind, not hers, that leaves are "like the things of man," a hackneyed Romantic cliche that should put readers immediately on guard. Our speaker is an impressive lyrical musician, but as a poet he is here considerably less impressive than his author.
Ah! as the heart grows older
It will come to such sights colder
By and by, nor spare a sigh
Though worlds of wanwood leafmeal lie;
In the eighth line, our speaker becomes a poet worthy of his worldly creator: those wanwood worlds lying leafmeal rank among Hopkins's most impressive creations. But we should not allow their imagistic music to deafen us to the drama playing out in these lines. The depressive speaker here confesses the condition of his melancholic soul. His once fresh thoughts have been dried by life to wrinkly raisins, and his sole defense against the unadulterated mind of a child is to imaginatively adulterate that mind, projecting his own present melancholy into the child's future.
And yet you will weep and know why.
The italicized word punningly displays (in an admirably Shakespearean way) the violent force of the speaker's sadistic will. He insists, with all the force of Victorian patriarchy, that his imaginings will be the child's future. To say it in Jargonspeak: he will interpellate the child into his discourse of depression. Father-figure knows best. No alternative futures need apply.
Now no matter, child, the name:
Sorrow's springs are the same.
The melancholic consciousness (that of the speaker and of his projected adult-child) is trapped in a mind of perpetual autumn where the names of seasons are so many Hamletian "words, words, words." The speaker's work of projection is now so complete (in his own mind) that he can adopt a tone of commiseration, of fellow-suffering. This may have been his motive all along. Misery does indeed love company, and it's more infectious than the plague.
Nor mouth had, no nor mind, expressed
What heart heard of, ghost guessed:
The deepest and most pathetic/bathetic truth of depression can be neither verbalized nor consciously known. It can only be expressed by the emotions and hypothesized to exist in the unconscious--'guessed' at in the ghostly self. Hopkins in these lines is a jaw-droppingly exact precursor of psychoanalysis.
It is the blight man was born for,
It is Margaret you mourn for.
Something as common (in all senses of the word) as self-pity lies at the core of a blighted consciousness that compulsively projects its blight even upon the greenest of worlds. In this final and mutedly triumphant psychological imposition, the speaker projects his blasted, self-pitying cinder-self upon the child. Her mind is still Romantically fresh, capable of being moved by nature; it is the adult speaker's mind, expressed in his projections, that has sealed itself into a self-perpetuating, self-pitying mantrap of grief in which nature, like his self, is a constant dying until cessation of breath brings its terminal literalization. His life can be described in a blasphemously liturgical formula: Death without end, amen. His only relief is the power-rush accompanying compulsive acts of cruelty such as the one dramatized here: the powerful projection of his living death into the mind of a child. The poem dramatizes a kind of mental molestation.