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)

36. People who have separated faith from love do not even know what faith is. When they do entertain an idea about faith, some of them see it only as mere thought, others as thought directed towards the Lord, and a few as the doctrine of faith. But faith involves not only knowledge of all the things that the doctrine of faith embraces and the acknowledgment of them; it is first and foremost obedience to everything that doctrine teaches. The primary point that it teaches for men's obedience is love of the Lord and love of the neighbour. Whoever is devoid of this is devoid of faith, a point which the Lord teaches so plainly in Mark as to leave absolutely no room for doubt,

The first of all the commandments is, Hear, O Israel, the Lord our God is one Lord. Therefore you shall love the Lord your God with all your heart, and with all your soul, and with all your mind, and with all your strength. This is the first commandment. The second is also like it, You shall love your neighbour as yourself. There is no other commandment greater than these. Mark 11:28-33.

In Matthew, He calls the former 'the first and great commandment', and says 'on these commandments the Law and Prophets depend', Matthew 22:35-40. The Law and the Prophets are the doctrine of faith in its entirety and the whole of the Word.