Will the Fruits Attained by the Lesser Vehicle Regress?

When a fourth-fruition arhat returns to the mundane world, he may regress from the fourth fruit back to the third fruit; after renouncing worldly life again and distancing himself from the secular world, he once more becomes a fourth-fruition arhat. If a fourth-fruition arhat can regress, the third fruit can certainly regress as well. Meditative concentration (samādhi) can also vanish, and mental activities can regress. Even a once-returner can fall back to stream-entry. If a fourth-fruition arhat, having eliminated grasping, can still regress and give rise to grasping again, how much more so the third fruit.

There are concrete examples in the Buddhist scriptures as proof. Without having attained that fruit, one cannot understand it. Standing at a lower level, one cannot see clearly the higher level, nor can one comment on it. Grasping the true facts can only be achieved through personal experience. It is just like many people today who, clearly still at the stage of ordinary beings (pṛthagjana), spend all day debating the realms of the Buddha-ground, arguing until red in the face—all of it mere armchair theorizing, utterly meaningless.