An Expensive Lesson.

From what little they know about his Supreme Law, the first sage has positioned himself as the fate of all beings. Unlike Soverick's use of fate, which limits him to seeing fate, the first sage has turned himself into a figure that can decide the fate of others. 

If the first sage determines the fate of someone, the destiny of that person has been changed. They will bring to pass the declaration of the first sage, regardless of how they resist.

If the destination has been set, then it doesn't matter which road they take or how long they take to reach it, they will meet this destination when the journey ends. Then they will find the first sage waiting there for them even if they are world gods. 

That's what the eye of the sage is. It is an eye that sees the multitudes of fates, locks on to one of them, and fixes it for the future. Then it uses everything available to bring about that fixed future.