I voted plot with surety. It, to me, is the penultimate example of the ruin that comes from human pride, and when Man thinks himself to be God. This is similar to the folly of Eden, notice? Man attempts to be like God, Man is struck down and reminded who they are, and that they are mortal. It is a very old lesson - Gilgamesh too comes to the conclusion that immortality is not something one can attain - and as such it struck me as the best of all things regarding Zeal, because it is so pertinent and real, and so well echoes humanity. It shows the fate of all empires, the fate of Man's works, and what happens if we trust too dearly in our own edens. Well, that is what I took from it. Power leads to Pride, and Pride leads to ruin. Zeal lacked contentment, though it held absolute understanding and learning. It is the same danger that lies before us nowadays, actually, and a moralistic lesson not to strive too greatly after things of our own making and learning, else in pride we will be destroyed.
A very Christian lesson, actually, and I was surprised to see it made use of in Chrono Trigger.