'A seed' signifies the ultimate and primary levels in a person. It also signifies good and truth from the Lord. In an opposite sense, it signifies falsity of doctrine and hellish falsity. 'A seed' signifies everyone who constitutes the Lord's spiritual kingdom and faith grounded in charity.

In Genesis 12:7, 8:15, 16, 'a seed' signifies love and everyone who has love.

(References: Arcana Coelestia 1025)

38. Verse 18 And to have dominion over the day and the night, and to make a distinction between the light and the darkness; and God saw that it was good.

'The day' is used to mean good, and 'the night' evil. Consequently goods are called 'the works of the day', whereas evils are called 'the works of the night'. 'The light' is used to mean truth, and 'the darkness' falsity, just as the Lord says,

Men preferred darkness rather than light; he who does the truth comes to the light. John 3:19-21.

Verse 19 And there was evening, and there was morning, a fourth day.