Considering that the fake edict actually is made on the 30th of March 315 (suposed date of the text), Licinius (that was emperor in the east) sees it as a sign that Constantine is a complete idiot and probably mad.
The Senators, after laughing like madmen for a week, go to Licinius and offer him the loyalty of the, vastly pagan, western legions.
Constantine, now emperor of nothing, is imprisoned and executed.
Because the edict favored the Christians, Licinius will think that the cristian "sorcerers poised" Constantine's spirit and declares chrisianity banned and orders more persecutions.
Two thousand years latter Constantine is remembered as a Mad Emperor and Licinius is seen as a great roman Emperor.