維摩經玄疏 6.66

6.66

Second, explaining that the four doors of the distinctive teaching and the four doors of the perfect teaching enter the substance of the true nature of the true mark: entering through their respective four doors, they perceive the true mark of buddha-nature and attain eternal nirvāṇa; in this they are identical. Although the principle is identical, the doors differ: since the doctrinal doors have the distinction between the partial and the perfect, there is the difference between the two kinds of four doors that can provide access. Because the true principle of buddha-nature is non-dual, the substance of the true nature to which access is gained is one. For example, the palace citadel has four gates; although the gates are not the same, the Son of Heaven who is seen is one. The four doors of the distinctive teaching are like entering from the four side gates of the palace citadel; the four doors of the perfect teaching are like entering from the four main gates. Although the side and main [gates] differ, entering to perceive the liberation of the true nature and the substance of the true mark is identical.