Maybe going line-by-line, to elicit various responses to what the words mean to our readers. It's two sentences and perhaps explaining each sentence separately, with a conclusion at the end, might work.
First, an image to work from:
Blossom:
[
en.wikipedia.org]
Fruit:
[
en.wikipedia.org]
Let's see...
Sullen and sinister, darkly dull of leaf,
Thou rearest amid the brighter flowers,
Like a presage of evil in dreams of joyance—
Evil of beauty thy blossoms,
And purple like the agony of Death,
And their fruit as its livid consummation.
A direct poetic address to the actual flower, itself, as it might be seen by a by-passer as s/he walks thru a garden of otherwise innocuous flowers.
The observer then links his/her knowledge about the toxic nature of the flower to a general observation of ironic comparison to a foreshadowing of jarring evil in an otherwise benevolent existence.
CAS expands this initial observation and association with evil amidst the ordinary--even beautiful--to the shade of the blossom, which he portrays as "funereal", and further links the appearance of the fruit to an implied physical description of being very much like postmortem lividity, or even advanced corruption.
With this developed image he now extends the metaphor...
Such a flower art thou
As might spring from the rotting of ancient sin,
Its unavoidable latter confession,
Or from the corroded altar-stone,
Now merged with the blood of its victims—
A hideous and fruitful wedlock—
In some place of sacrifice to monstrous gods.
He now compares it to the idea of primal, perhaps universal, sin, by creating the image that the flower is rooted in the very idea of sin, and hence evil. He further observes that the visual manifestation of the flower is like a stain or stigmata that is apparent to all, and hence "unavoidable" or undeniable. Like evident sin, it's out there to see, and one can "see" it for what it is.
It's worthy of note that this particular comparison to sin is intangible--comparing the flower to a concept, and not to another tangible object. This is because he goes on to form a final, concrete comparison.
He now focuses on the concept of human or animal sacrifice--although I think we can safely assume human, this being CAS, after all!--as a concrete example of sin. Here. too, CAS implies that flower is rooted in a physical manifestation of evil--this time in a sort of imagined humus of years of blood-letting onto an altar stone. And to top it off, this is no Abrahamic deity, seeking its--AHEM!--just worship, but is more along the lines of Thasaidon and his ilk.
WHEW!
OK, to me the poem is in the form of a standard poetic observation, comparison, rumination, and development of a metaphoric analogy where the the poet receives an initial impression from a fairly commonplace object and extends it for philosophic resonance.
What say ye?
--Sawfish
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"The food at the new restaurant is awful, but at least the portions are large."
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