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)

3814. 'And he dwelt with him for a full month' means a new state of life. This is clear from the meaning of 'dwelling' as life, dealt with in 1293, 3384, 3613, and from the meaning of 'a full month' as a new state. All periods of time mean states, see 1274, 1382, 2625, 2788, 2837, 3254, 3356, 3404, so that years, months, and days mean such. What kind of states are meant however is clear from the numbers attached to them. When however year, month, or day is used in the singular, an entire state is meant, and so the end of the previous state and the beginning of the next, as has also been shown in various places in the explanations. Here therefore 'month' means the end of the previous state and the beginning of the next, and so means a new state, as in other places in the Word, as in Isaiah,

At length from month to its month, and from sabbath to sabbath, all flesh will come to bow down before Me, said Jehovah. Isaiah 66:23.

In John,

He showed me a pure river of the water of life, bright as crystal, flowing from the throne of God and of the Lamb. In the middle of its street, and of the river, on this side and on that, was the tree of life bearing twelve fruits, yielding its fruit each month. Revelation 22:1-2.

'Yielding its fruit each month' stands for a state for ever new as regards the reception of good and the consequent practice of it. In Moses, Count the sons of Levi according to their father's house and according to their families. Every male a month old and over shall you count. Count every firstborn male of the children of Israel, a month old and over, and take the number of their names. Numbers 3:15, 40.

[2] It was because the end of the previous state and the beginning of the next, that is, a new state, was meant by 'a month' that they were ordered to count those who were 'a month old and over'. In the same author,

If you see among captives a beautiful woman, and have a desire for her so that you would take her to yourself for a wife, she shall remove the clothing of her captivity from upon her, and she shall sit in your house and lament her father and her mother for a full month. After that you shall go in to her and know her, and she shall be your wife. Deuteronomy 21:11, 13.

Here 'a full month' clearly stands for the end of the previous and the beginning of the next or new state.