摩訶止觀 5.16

5.16

此十種境，始自凡夫正報，終至聖人方便。陰入一境常自現前，若發、不發，恒得為觀；餘九境，發可為觀，不發何所觀？又八境去正道遠，深加防護，得歸正轍；二境去正道近，至此位時不慮無觀，薄修即正。

These ten kinds of realms begin with the direct retribution of ordinary beings and end with the expedients of the sages. The single realm of the aggregates and sense fields is constantly present before us; whether it has been aroused or not, it can always serve as [an object of] contemplation. As for the remaining nine realms, when they are aroused, they may serve as [objects of] contemplation, but if they are not aroused, what would there be to contemplate? Furthermore, eight of the realms are far removed from the right path, so that if one guards against them carefully, one can return to the correct track; two of the realms are close to the right path, and when one reaches this stage, one need not worry about lacking contemplation—with slight cultivation one is corrected.