A number of discourses (among them, SN 35.191; AN 6.63) make the point that the mind is fettered, not by things like the five aggregates or the objects of the six senses, but by the act of passion & delight for them. There are two ways to try to cut through this fetter. One is to focus on the drawbacks of passion & delight in & of themselves, seeing clearly the stress & suffering they engender in the mind. The other is to analyze the objects of passion & delight in such a way that they no longer seem worthy of interest. This second approach is the one recommended in this discourse: when the Buddha talks of "smashing, scattering, & demolishing form (etc.) and making it unfit for play," he is referring to the practice of analyzing form minutely into its component parts until it no longer seems a fit object for passion & delight. When all five aggregates can be treated in this way, the mind is left with no conditioned object to serve as a focal point for its passion, and so is released at the very least to the stage of Awakening called non-return.
I have heard that on one occasion the Blessed One was staying near Savatthi at Jeta's Grove, Anathapindika's monastery. Then Ven. Radha went to the Blessed One and, on arrival, having bowed down to him sat to one side. As he was sitting there he said to the Blessed One: "'A being,' lord. 'A being,' it's said. To what extent is one said to be 'a being'?"
"Just as when boys or girls are playing with little sand castles: as long as they are not free from passion, desire, love, thirst, fever, & craving for those little sand castles, that's how long they have fun with those sand castles, enjoy them, treasure them, feel possessive of them. But when they become free from passion, desire, love, thirst, fever, & craving for those little sand castles, then they smash them, scatter them, demolish them with their hands or feet and make them unfit for play.
4. Lit.: "dirt houses."