Darkness" is a state without light. "Light" is truth from the Lord, so "darkness" represents a state where truth is lacking. Here's a cogent passage from Arcana Coelestia: "The person who has yet to be regenerated is called 'a void and an empty earth', and also 'ground', in which no good or truth at all has been sown - 'void' where there is no good, and 'empty' where there is no truth. Consequently there is 'thick darkness', or stupidity and lack of knowledge about anything that has to do with faith in the Lord and so anything that has to do with spiritual and celestial life. (Arcana Coelestia 17)

27. Verse 9 And God said, Let the waters under heaven be gathered together to one place, and let the dry land appear; and it was so.

Once a person knows of the existence of the internal man and of the external man, and knows that, contrary to appearance, truths and goods flow in from the internal man, or from the Lord by way of the internal into the external, then the things residing in him as cognitions of truth and good are stored away in his memory and registered among the facts there. For anything that finds its way into the memory or the external man, whether natural, spiritual, or celestial, lodges there as known fact, and from that place it is brought out by the Lord. These cognitions are 'the waters gathered together to one place' and are called 'seas'. But the external man itself is called 'the dry land' and immediately afterwards 'earth', as in the verses that follow.