615. And like the voice of loud thunder. This symbolizes the Lord speaking through the new heaven out of Divine love.

Lightnings, thunderings and voices symbolize enlightenment, perception and instruction, as may be seen in no. 236. And seven thunders speaking symbolize the Lord's speaking through the whole of heaven (no. 472).

When the Lord speaks through heaven, He does so from the third heaven through the second heaven, thus from love through Divine wisdom, for the third heaven is impelled by His Divine love, and the second heaven by His Divine wisdom. The Lord never speaks in any other way when He speaks from the higher heavens. This, then, is what is meant by a voice like the voice of many waters, and by a voice like the voice of loud thunder. Many waters are the Divine truths of Divine wisdom, and loud thunder is the Divine goodness of Divine love.

In Exodus 9:23, 29, this signifies truths divine which enlighten and perfect people in heaven, but terrify people in hell. (Arcana Coelestia 7573)

In Psalm 29:3, this signifies the Word in its power. (Doctrine Regarding Sacred Scripture 18[4])

When the Lord speaks through the heaven, it descends into the lower spheres and is heard as thunder. As He speaks through the whole of heaven at once, the sound is called 'seven thunders' in Revelation 10. 'Seven' signifies all, everything, and wholeness. This is why 'thunder' signifies instruction and perception of truth, and in this instance, the revealing and manifestation of truth. A voice from heaven is heard as thunder when it comes from the Lord, which can be seen in John 12:28-30, Job 37:4-5, 2 Samuel 22:14, Revelation 14:2, and Psalms 81:8. 'Great thunder,' as in Revelation 14:2, signifies the divine good of divine love.

(References: Apocalypse Explained 10, 14 [2]; Apocalypse Revealed 472)