User blog comment:IamJakuhoRaikoben/Sorcerer Magazine, Issue 34: October 2014/@comment-1776824-20141101080224/@comment-1776824-20141101170823

Strength doesn't necessarily mean physical strength. Strength of the heart, which was supposed to reference Makarov~ And their souls not wavering was a reference to Jura's almost obsessive desire to fight Laxus and fighting even though he knew he was most assuredly going to lose in the end.