486. Verse 4 And the days of Man after he beget Seth were eight hundred years; and he beget sons and daughters.

'Days' means periods of time and states in general. 'Years' means periods of time and states in particular. 'Sons and daughters' means the truths and goods that they perceived.

The creation of heaven and earth in the first chapter of Genesis represents the new creation of the celestial church called 'Man'.

(References: Arcana Coelestia 9336, Genesis 1)