353. And I heard one of the four animals saying as with a voice of thunder. That this signifies, out of the inmost heaven from the Lord, is clear from the signification of the four animals or cherubim, as denoting, in the highest sense, the Lord's Divine Providence and protection lest any one should approach except through the good of love (concerning which see above, n. 152, 277); and [as denoting], in a respective sense, the inmost and third heaven (concerning which also see above, n. 313, 322); and from the signification of a voice of thunder, as denoting manifestation thence. That by lightnings, thunderings, and voices in the Word, are signified enlightening, understanding, and perception, may be seen above, n. 273, hence also manifestation. That thunders signify manifestation out of the inmost heaven is from correspondence; for the voices which flow down out of that heaven even into the hearing of man, are not otherwise heard, for they fill the whole brain (cerebrum), and thence propagate themselves towards the hearing, and are there perceived by such a sound. It is different with the voices that flow down out of the middle heaven. These, since they flow in with enlightenment, are therefore heard sonorously like the expressions of speech.

[2] The reason is, because the things that flow down out of the inmost or third heaven enter man's Voluntary, and the Voluntary is made known by sounds; but the things that flow down out of the middle or second heaven, enter into man's Intellectual, and the Intellectual is made known by the articulations of sound; for sounds are formed in the understanding; and sounds formed, which are called its articulations, manifest themselves by ideas in the thought, and by expressions in the hearing. Hence it is that those things that flow down out of the inmost or third heaven correspond to thunder, and those out of the middle or second heaven to lightning; and hence also it is that in the Word, by lightnings and thunderings are signified enlightenment, understanding, and perception. These have a likeness with sounds in the world, which increase when they descend from heights, as from high mountains into valleys, and also as when from the clouds towards the earth, whence thunderings [are heard]; thus also the voices out of the third or highest heaven, when they are rolled towards the lower parts, and at length into the lowest, in which is human hearing, are heard as thunderings, but only by those who have their interiors opened, as John's then were.