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.

Water in the Bible represents true ideas about natural, external things – day-to-day life and physical existence. The sea represents the whole collection we have of these natural truths (to use a common term from the Writings). Those representations – like all other representations in the Bible – can be negative as well as positive; the water in the sea can also represent false thinking and twisted logic. This is especially true when a storm stirs up the sea and causes waves; the waves represent arguments which come from false and twisted thinking and which attack our belief in what's true. In most cases this comes in the form of temptation, when false thinking attempts to link up with our evil desires and convince us that it's OK – and even good – to go ahead and do what we want.

(References: The Apocalypse Explained 419 [23-24], 538 [5])