2449. That 'He overthrew those cities' means that all truths were separated from them so that they might possess falsities alone is clear from the meaning of 'cities' as matters of doctrine, and so as truths, for truths make up matters of doctrine, dealt with in 402, 2268, 2428. These are said to be 'overthrown' when falsities stand in place of truths, here when all truths have been separated from them, as well as all goods - goods too being dealt with in this verse, since the subject is the final state of those inside the Church who are governed by falsities and evils.
 This also is what their state comes to be, which, so that the nature of it may be known, must be described briefly. All who enter the next life are taken back to a life similar to that which they were leading during their lifetime., Then in the case of the good evils and falsities are separated so that the Lord may raise these people up by means of goods and truths into heaven; but in the case of the evil goods and truths are separated so that those evil ones may be carried away by means of evils and falsities into hell, see 2119, in exact accord with the Lord's words in Matthew,
To him who has, it will be given, so that he may have more abundantly; but from him who has not, even what he has will be taken away. Matt 13: 12.
And elsewhere in the gospel,
To everyone who has, it will be given, so that he may have in abundance; but from him who has not, it will be taken away. Matt 25: 29; Luke 8: 18; 19: 24-26; Mark 4:-24, 25.
The same is meant by the following words which appear in Matthew,
Let both grow together until the harvest; and at the time of harvest I will tell the reapers, Gather the weeds first and bind them in bundles to burn them, but gather the wheat into my barn. The harvest is the close of the age. Just as the weeds are gathered and burned with fire, so will it be at the close of the age. Matt 13: 30, 39, 40.
The same point is made in the description of the net thrown into the sea gathering fish of various kinds, and how after that the good were sorted into vessels while the bad were thrown away; and this is how it will be at the close of the age, Matt 13: 47-50.What 'the close' is and that for the Church it entails events like these, see 1857, 2243.
 The reason why evils and falsities are separated in the case of people who are good is that the latter may not be left suspended between evils and goods and so that they may be raised up by means of goods into heaven. And the reason why goods and truths are separated in the case of the evil is so that they do not lead the upright astray by means of any goods present with them, and so that by means of their evils they may withdraw to the evil in hell. For in the next life such is the communication of all ideas comprising thought, and of all affections, that goods are communicated with the good, and evils with the evil, 1388-1390. Consequently unless separation took place countless harmful things would result, in addition to the fact that association together would not otherwise be possible. Yet all things are associated together in a very wonderful way, in heaven according to all the variations of love to the Lord and of mutual love, and consequently of faith, 685, 1394, and in hell according to all the variations of evil desires and of delusions resulting from these, 695, 1322. It should be recognized however that separation does not mean complete removal, for nothing anybody has once possessed is totally removed from him.