For more information on the “Sijjin”, please see Chapter 83 – Surah Al Mutaffifin (The Defrauders), verses 7-9.
You may wish to read Surah Al Zalzala along with this surah.
This concludes Surah Kahf. The first two questions asked by the Meccans were answered by verses from this Surah. The final question, regarding “Ruh”, was answered in Surah 17, verse 85.