人心一念 A Single Thought
大聖道：「我已知悔了，但願大慈悲指條門路，情願修行。」這才是：大圣道：「我已知悔了，但愿大慈悲指条门路，情愿修行。」这才是：
逐句解 Line by line
The Great Sage said: “I already know repentance; I only beg the greatly merciful one to point me a path, and I will gladly cultivate myself.” This was indeed a case of:
這才是 introduces the closing couplet-verse.
Let the human heart give rise to a single thought,
一念 — “a single thought”; 一 takes yí before fourth-tone 念.
and Heaven and Earth will know it through and through.
The couplet's claim is jurisdictional: a single thought is already known to heaven and earth, so there is no interval in which an intention is private.
If good and evil met with no requital,
The conditional is rhetorical and the next line will refuse it. 善惡 pairs the two in the order the maxim requires, good before evil.
then the cosmos itself must harbor partiality.
乾 is qián in 乾坤, the trigram, not the gān of dryness. The line completes the conditional the couplet before it opened, and answers it by reductio: if good and evil went unrequited, the cosmos would be partial — which it is not.
The monkey relents. His declaration — 我已知悔了, “I already know repentance” — is the hinge of his whole arc, the moment defiance yields to the wish for a path. The narration marks its weight with a four-line verse on the moral transparency of the cosmos.
The couplet is one of the novel's clearest statements of its moral metaphysics: a single thought of the heart is known at once to Heaven and Earth, and good and evil must meet their requital, or the universe would be unjust. Following Anthony C. Yu, the verse universalizes the monkey's private turn into a cosmic law — his repentance is registered instantly, and his redemption thereby assured.
Plaks reads the moment as the true climax of the chapter's spiritual argument. Everything since the opening lyric has bent toward this: the unruly xīnyuán, having exhausted rebellion, at last forms the one right intention, and the machinery of salvation — pilgrim, fillet, and journey — can now be set in motion to meet it.