Lyric discussion by freshonlybakery 

Cover art for Pyro lyrics by Kings of Leon

I was confused over the 'cornerstone' bit and looked it up. According to online dictionaries a cornerstone can be either;

explanation - thought that makes something comprehensible meat and potatoes - the fundamental part; "successful negotiation is the meat and potatoes of arbitration" supposal, supposition, assumption - a hypothesis that is taken for granted; "any society is built upon certain assumptions"

Song Meaning

Something that might be of worth... Jesus in the Bible is referred to the cornerstone in the Bible, and given KOL's background, they are probably aware of this.