The Islamic State Seeks the Battle of the Apocalypse (link)

Clarion Project

The gruesome video released by the Islamic State (ISIS or ISIL) emphasizes that the beheading of Peter Kassig took place in the town of Dabiq, Syria. The town was chosen because of its significance in Islamic end-of-time prophecies about the time when the Mahdi

MahdiGlossary Item

The Mahdi is a figure who, according to certain Islamic believers, will unify Mankind under Islam after vanquishing a false messiah; Shiites sometimes refer to him as the "Hidden Imam."

and (the Islamic version of) Jesus will bring victory over those who oppose sharia

ShariaGlossary Item

A legal framework to regulate public and private aspects of life based upon specific Islamic teachings. Sharia is a strict system which views non-Muslims as second-class citizens, sanctions inequality between men and women and prescribes cruel and unusual punishments for crimes.

 

The Islamic State named its English-language magazine "Dabiq" for the same reason. The group is telling Muslims that it is fulfilling prophecy, enticing them to participate in one of the most important moments in world history.

A secondary message is that Islamic State supporters should not worry about the military superiority of their enemy or the terrorist group's setbacks because they will soon be made victorious with help from the Mahdi, Islam's messianic figure, and Jesus (when he joins Islam, which he will according to Islamic prophecy).

much more here http://www.clarionproject.org/analysis/dabiq-islamic-state-wants-battle-end-days