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22 Over the head of the living creature there was the likeness of an expanse, like the awesome crystal to look on, stretched forth Over their heads above.
18 It was made with cherubim and palm trees; and a palm tree was between cherub and cherub, and every cherub had two faces;
The firmament of heaven represents mutual love. The firmament, as in Genesis 1, signifies the internal man.
(Odkazy: Arcana Coelestia 24)