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)

5869. 'And Joseph could not contain himself before all those standing with him' means that now everything had been prepared by the internal celestial for the joining together. This is clear from the representation of 'Joseph' as internal good, dealt with in 5805, 5826, 5827, thus the internal celestial, for the expression 'the celestial' is used to mean good that emanates from the Lord; and from the meaning of 'not being able to contain himself' as the fact that everything had been prepared for the joining together. For when someone prepares himself most eagerly to achieve some end or effect, by seeking out and organizing the means to achieve it, he can no longer contain himself once all the preparations are complete. This is the meaning of the words under consideration here. For the chapter before this dealt with the initial steps that were taken to achieve the joining together, whereas the present chapter deals with the actual joining together, see 5867. 'All those standing with him' means the kinds of things which prevent the joining together and which were therefore cast away, as stated in what follows.