法華義疏 6.28

6.28

既以疑情故索，疑是解津，若有解津則大機已動，扣佛說一，即是索一，故後賜一也。

Since they requested due to a state of doubt, and doubt is the ford to understanding, when there is a ford to understanding, the great capacity has already been stirred. Prompting the Buddha to speak of the one is itself requesting the one; hence one is subsequently bestowed.