Merpersons

[-JKP-]

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In any case, I suggest the mermaid imagery depicts the "ruling over Rahab", a Hebrew seamonster representing chaos, who is mentioned in Psalm 89 (which is a bit water heavy in any case) - the image shows the human essence of the monster being lifted away from the beast in God's good light.
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If the imagery is based on Frankish/Gallic legends of Mélusine/Melucina then the separation of the fish and the woman might be due to the fact that she stepped in and out of her fish role/persona on Saturdays, the day she bathed.