維摩經玄疏 1.80

1.80

第四、明起三觀者，即是用四悉檀起三觀也。夫至理幽絕，不可以智知，不可以識識，豈修觀行而能契會者哉！自非悉檀之巧妙，豈能用三觀會三諦之理也。

Fourth, clarifying generating the three contemplations: this means using the four siddhāntas to generate the three contemplations. The ultimate principle is dark and transcendent; it cannot be known by wisdom, nor can it be recognized by consciousness. How could one harmonize with it merely by cultivating contemplative practice! Were it not for the skillful subtlety of the siddhāntas, how could one use the three contemplations to harmonize with the principle of the three truths?