大般涅槃經義記 7.225

7.225

第四門中，心淨列名，次辯其相，「有漏不淨」舉穢顯淨，「佛無漏」下彰淨異穢，「以大淨」下將義顯體，成涅槃大，「是名初德」總以結之。

In the fourth section, purity of mind is listed by name, and next its characteristics are discriminated. "The defiled is impure" adduces defilement to reveal purity. From "The Buddha is undefiled..." onward, it displays that purity is distinct from defilement. From "Because of great purity..." onward, meaning is taken up to reveal the essence, establishing the greatness of nirvāṇa. "This is called the first virtue" concludes it overall.