In Revelation 14:2, 'the voice of great thunder' signifies the Lord speaking through the New Heaven from Divine Love; it also signifies a glorification of the Lord from His celestial kingdom. (Apocalypse Revealed 615, Apocalypse Explained 855)

'Voices,' 'lightnings,' and 'thunders,' as in Revelation 16:18, signify rationalizations, falsifications of truth, and arguments grounded in falsities that stem from evil in the church among people who believe in salvation by faith alone. (Apocalypse Explained 821[4], 1014)

(References: Apocalypse Revealed 710)

710. 16:18 And there were voices and lightnings and thunderings. This symbolizes reasonings, falsifications of truth, and arguments in consequence of the falsities accompanying evil among people caught up in faith alone, who refuse to reflect on the evils in themselves, since they would not want to turn away from those evils if they were to know them.

Voices, lightnings and thunderings symbolize reasonings, falsifications of truth, and arguments in consequence of falsities, as can be seen from what we said above in nos. 396, 530, and the same words there.

Regarding people caught up in a faith divorced from works of the law, who consequently engage in evil practices, that they refuse to reflect on the evils in themselves, because they would not want to turn away from those evils if they were to know them, is apparent without explanation. Experience shows this. For evils are delightful, because they are expressions of love, and no one want to turn away from things that delight him unless he gives thought to life after death, first to hell and what it is like, and then to heaven and what it is like, and thinks about them when not engaged in the doing of evil. If he also then turns to the Lord and thinks, "What is something temporal in relation to eternity? Is it not as nothing?" it is then that he can reflect on his evils, with a willingness to see them and turn away from them.

But if a person has first confirmed himself in faith alone, he will then say in his heart, "Our theological faith, that God the Father takes pity on us for the sake of His Son who suffered for our sins - if I make appeal to it with some degree of trust, that faith does all the rest." He then does not reflect on any evil in him. He also says to himself because of that faith that evil does not condemn, that salvation is a matter of pure mercy, and other like things. Thus he remains engaged in his evils and finds delight in them to the end of his life.

Such are the reasonings, falsifications of truth and arguments in consequence of falsities accompanying evil that are here symbolically meant by voices, lightnings, and thunderings.