法華玄贊義決 1.40

1.40

四欲說三淨法門故，眾生本性未曾垢淨，於眾生顛倒故成垢淨，垢重不可頓拔故。佛菩薩漸漸出之以開三淨：一以五戒十善淨三途，二說二乘以淨三界，後明一乘以淨三乘。以三途為重苦，三界為中苦，變易生死為下苦，故說三淨。

Fourth, because [the Buddha] wished to teach the dharma gates of the three purifications. The original nature of sentient beings is neither defiled nor pure; because of sentient beings' inversions, defilement and purity are formed. Because heavy defilements cannot be eradicated all at once, the buddhas and bodhisattvas gradually draw them out so as to open the three purifications: 1. Purifying the three wretched destinies with the five precepts and ten virtues; 2. Preaching the two vehicles to purify the triple realm; 3. Subsequently illuminating the One Vehicle to purify the three vehicles. Considering the three wretched destinies as severe suffering, the triple realm as middling suffering, and the death of inconceivable transformation as minor suffering, the three purifications were taught.