Sam_Ellis can be very transparent in her writing. Most of the decisions she makes are often very obviously made to serve the plot and give Aurelius a way to succeed as can be expected of practically any Author.
Aurelius wasn't strong enough to simply fight his way through the first trial, so Samantha wrote it so he could progress. And of course, when it came to destroying the Blood, she needed to write in a way for Aurelius to succeed where Viktor, who was stronger and smarter than him, had failed.
The answer lay in Aurelius being a godling who possessed Divine Energy.
Aurelius was stumped on the problem of destroying the Blood but once he mentioned Divine Energy and Conscience just stared back uncomprehending, he realized Viktor may not have actually considered every possible avenue when he was trying to destroy the Blood.
And so, Divine Energy became the foundation on which Aurelius built a destructive spell specialized for undoing the Blood at its very core.
