大方廣圓覺修多羅了義經略疏 2.1198

2.1198

感應也，或見佛像、或覩光明。不作聖心名善境界，若作聖解即墮群邪。故下文云：「非彼所聞，一切境界終不可取。」若天台意，即與信等相應，名善境界。

This is sympathetic resonance: either seeing a buddha image or beholding bright light. If one does not form a holy conceit, it is called a good state; if one interprets it as holy, one falls into various heterodoxies. Hence the text below states: "All realms that are not what they have heard must never be grasped." According to the Tiantai view, being congruent with faith and the like is called a good state.