法華義疏 2.302

2.302

凡有二義：一、欲歎佛神通希有，即是歎於佛乘令四乘之人欣慕；二者、欲表說一乘故歎一光也。

Generally there are two meanings: First, it intends to praise the Buddha's supernatural powers as rare, which is praising the Buddha vehicle to cause people of the four vehicles to yearn for it; second, it intends to signify the expounding of the ekayāna, hence it praises the single ray of light.