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18 And to rule over the day and over the night, and to divide the light from the darkness: and God saw that it was good.
"Birds" represent rational concepts in the external man and intellectual concepts in the internal man.
15 and it happened, when Pharaoh would hardly let us go, that Yahweh killed all the firstborn in the land of Egypt, both the firstborn of man, and the firstborn of animal. Therefore I sacrifice to Yahweh all that opens the womb, being males; but all the firstborn of my sons I redeem.'