金光明經文句記 4.145

4.145

初、約蛇報明四相。蛇有力敵羸絕等報，可譬身有生老病死增減四相。

First, explaining the four marks in terms of the serpents' retributions. Serpents have retributions such as having matched strength, being emaciated, or dying, which can serve as a metaphor for the body having the four marks of increase and decrease: birth, old age, sickness, and death.