The concept had been mentioned explicitly already in Revelation 18:3 and implicitly in Revelation 18:11–13. By repeating the matter the Holy Spirit underlines what motivated these merchants in their business ventures; it was all about personal enrichment (selfishness). That explains their “weeping and mourning aloud,” mentioned at the end of Revelation 18:15 as repetition of Revelation 18:11.
15 The merchants of these wares, who gained wealth from her, will stand far off, in fear of her torment, weeping and mourning aloud,