The phrase is structured as two parallel clauses: “put down the weapon of evil,” and as a direct result, “instantly attain enlightenment.”
This idiom is deeply rooted in Zen (禅宗) Buddhism, which emphasizes the possibility of `顿悟 (dùnwù)`, or sudden enlightenment. Unlike schools of thought that propose a long, gradual path of accumulating good karma, Zen teaches that enlightenment can be achieved in a single, transformative moment of insight. `放下屠刀,立地成佛` is the ultimate expression of this belief. It argues that a person's intrinsic nature is pure (the “Buddha-nature”), and it is only obscured by ignorance and evil deeds (the “butcher's knife”). The moment one casts aside these obscurations, their true, enlightened nature is revealed. This reflects a core cultural value in East Asia: the profound belief in human potential for radical change and the importance of repentance.
This chengyu is formal and carries significant weight. It's not used for trivial matters.