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7 And God made the firmament, and divided the waters which were under the firmament from the waters which were above the firmament: and it was so.
'A sandal tree' signifies aspects of the natural self.
(References: Apocalypse Explained 518)
20 Look at Zion, the city of our appointed festivals. Your eyes will see Jerusalem, a quiet habitation, a tent that won't be removed. Its stakes will never be plucked up, nor will any of its cords be broken.