611. But in the days of the voice of the seventh angel, when he is about to sound.- That this signifies the last state of the church, and then revelation of Divine Truth, is evident from the signification of the days of the voice of the seventh angel, as denoting the last state of the church; for the progressive changes of the state of the church are described by the sounding of the seven angels, therefore the voice of the seventh angel signifies the last state; and from the signification of, when he is about to sound, as denoting revelation then of Divine Truth. That by sounding a trumpet or horn is signified the influx of Divine Truth, and its revelation, may be seen above (n. 502). That its revelation is here signified, is evident from the following part of this verse, where it is said, "And the mystery of God shall be consummated, as he hath declared in good tidings to his servants the prophets." This signifies that the prediction concerning the coming of the Lord shall then be fulfilled. With the coming of the Lord there is also revelation of Divine Truth.

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)