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28 And God blessed them, and God said unto them, Be fruitful, and multiply, and replenish the earth, and subdue it: and have dominion over the fish of the sea, and over the fowl of the air, and over every living thing that moveth upon the earth.
"Birds" represent rational concepts in the external man and intellectual concepts in the internal man.
7 And you, be ye fruitful, and multiply; bring forth abundantly in the earth, and multiply therein.