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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.
19 All the firstborn males that are born of your herd and of your flock you shall sanctify to Yahweh your God: you shall do no work with the firstborn of your herd, nor shear the firstborn of your flock.