9  is the number of finality as well as Judgement and after the eternal victory of the 144,000 , it is time for the judgement of the fallen angels as well as all sinners. The Apostle Paul has stated that the saints will judge the fallen angels
http://www.biblestudy.org/bibleref/meaning-of-numbers-in-bible/9.html
http://www.biblegateway.com/passage/?search=%201%20Corinthians%206:%203&version=KJ21

and this theme is repeated in Revelation 20, those saints who rise from the dead in the first resurrection are also given Judgement at the commencement of the millennium.
http://www.biblegateway.com/passage/?search=Revelation%2020:4&version=KJ21