For Moroni, this part of the story—forming the secret combination—is crucial. In their later form as the Gadiantons, secret combinations will be the downfall of the Nephites, just as they would bring down the Jaredites. Moroni underscores the importance of this passage by making it the springboard for his moral editorial from verse 18 through verse 26, which is the end of the 1830 chapter as well as all editions after 1879.
The catalogue of evil actions (“murder,… plunder,… lie, and… all manner of wickedness and whoredoms”) is a staple in Mormon’s redaction, obviously borrowed here by Moroni. (See commentary accompanying Alma 17:14, 50:21, and Helaman 6:17.)