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)

'The former heavens, which passed away,' as mentioned in Revelation 21:1, signify the societies of people in the spiritual world who were only in external or apparent good. (Apocalypse Explained 675) Heavens are celestial and spiritual things. Consequently, they are inmost things, both of the Lord's kingdom in heaven and in the earth. This also refers to the church, and every individual, who is a kingdom of the Lord, or a 'church.' Consequently, heavens denote all things pertaining to love and charity, and faith grounded in them, as well as all things pertaining to internal worship. In like manner they denote all things pertaining to the internal sense of the Word. All these things are heavens, and are called, 'the throne of the Lord.' (Arcana Coelestia 2162)

(References: Apocalypse Explained 21)