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)

359. We could not be images of God according to his likeness unless he were within us and were our life from our very center. God's presence within us and God's being our life from our very center follow from what I explained in 4-6 above, namely that God alone is life and that we and angels are life-receivers from him.

The Word tells us that God is in us and makes his home with us; and because the Word tells us this, preachers are fond of telling us to prepare ourselves to let God come into our lives so that he may be in our hearts and that our hearts may be his dwelling. The devout say the same in their prayers. Some [preachers] talk and preach more explicitly about the Holy Spirit, who they believe is within them when they are filled with holy zeal as the source of their thought, speech, and preaching. I have explained in 51-53 of Teachings for the New Jerusalem on the Lord that the Holy Spirit is the Lord and not some God who is a separate individual. The Lord actually says, "In that day you will know that you are in me and I in you" (John 14:21 [20]), and he says similar things in John 15:24 [4] and John 17:23.