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14 And God said, Let there be lights in the firmament of the heaven to divide the day from the night; and let them be for signs, and for seasons, and for days, and years:
To be fruitful relates to goodnesses, and to be multiplied, truths.
(References: Arcana Coelestia 1014, 1018)
1 And it came to pass, when men began to multiply on the face of the earth, and daughters were born unto them,