法華義疏 3.206

3.206

現瑞通表說一經因果之義，唯佛能了，故窮學未知，所以疑也。正說中偏對身子，是執異之端，故生疑致請也。

The manifestation of portents generally signified the meaning of cause and fruit of the entire sūtra, which only Buddhas can fully comprehend; therefore even those of exhaustive study did not know it, which is why he doubted. In the main exposition, it is addressed specifically to Śāriputra, who was the foremost in clinging to divergence; therefore he gave rise to doubt and made the request.