You mean one could inflect "theou" in genitive but not inflect "stylos", and still refer stylos to theos? (I am using stylos and not the other noun and adjective because I am fairly sure of how to inflect stylos). I am not disputing you, just trying to improve my already nearly perfect Greek.
Be it as it may, it is a strange description of God as a pillar and ground, in a supporting role to truth.
Of course, other references to the Church (or at least the apostles) receiving the truth from the Holy Ghost still stand.
"You mean one could inflect "theou" in genitive but not inflect "stylos", and still refer stylos to theos? (I am using stylos and not the other noun and adjective because I am fairly sure of how to inflect stylos)."
I think so, yes. If stylos were an adjective, it would be different. I just don't see it being said that way. More likely one would say a clause beginning with tou. But then again, my Greek cousins tell me I speak Greek like a Spanish cow (same thing my French friends say about my French)! :)