The supreme good is the original substance of the mind.
"The supreme good is simply this mind being perfectly pure heavenly principle — how can it be sought in things?"
爱问：「知止而后有定，朱子以为『事事物物皆有定理』，似与先生之说相戾。先生于事事物物上求至善，却是义外也。至善只是此心纯乎天理之极便是，更于事物上怎生求？」
先生曰：「至善只是此心纯乎天理之极便是。何以于事物上怎生求？且如事亲，如何而为温凊之节、如何而为奉养之宜者，所谓定理也。此心纯乎天理之极，则凡所以温凊奉养者，莫非天理之发见。若只于事物上求之，则温凊奉养之事，一一须要安排停当，岂非义外之说乎？」
Xu Ai asked: "Regarding 'knowing where to rest,' Zhu Xi says all things have fixed principles. The supreme good is simply this mind being perfectly pure heavenly principle — how can it be sought in things?"
The Master said: "The supreme good is simply this mind being perfectly pure heavenly principle. How can it be sought in things? Take serving parents as an example — the rules for warming in winter and cooling in summer, the proper ways of attending and nourishing — these are what are called fixed principles. When this mind is perfectly pure heavenly principle, then all acts of warming, cooling, attending, and nourishing are nothing but manifestations of heavenly principle. If one seeks only in things, then each act of warming, cooling, attending, and nourishing must be arranged one by one — is this not the theory of righteousness being external?"
When facing complex tasks, instead of exhaustively studying every detail (seeking principle in things), first make your mindset and direction pure (this mind perfectly pure heavenly principle). When the mind is correct, priorities and methods become naturally clear.
"The supreme good is simply this mind being perfectly pure heavenly principle."
The supreme good is not a distant goal but the original face of the mind. The effort is not seeking outward but letting the mind return to its original substance — when the mind is refined to utmost purity, the supreme good naturally appears.
"If one seeks only in things, each act must be arranged one by one."
Yangming points out the practical difficulty of Zhu Xi's approach: if every matter requires exhaustive study of its principles, then serving parents requires studying warming principles, cooling principles, nourishing principles... endlessly. Yangming's solution is to return to the mind — when the mind is correct, behavior is naturally correct.