As rain does not penetrate a well-roofed house, so passion does not penetrate the well-cultivated mind.

The positive pair to the previous verse. Subhāvitaṃ — well cultivated: the same root as bhāvanā, meditation practice. A mind that has been worked, developed, that has known sustained discipline, has the solidity of a well-constructed roof.

Na samativijjhati — does not penetrate: it is not that passions do not exist or do not try to enter. It is that they find no gap through which to slip. The mature practitioner feels the pull of desire without being pierced by it; recognizes it, observes it, and returns to center without having lost balance.

This is a functional description of what in yoga is called vairāgya — detachment. Not cold indifference but the capacity to experience without being captured. Attachment and aversion are both forms of being governed by the external; vairāgya is the capacity to move in the world without the world moving the center.

The practice of sati (mindfulness) is the continuous roof repair work. Each moment of distraction is a potential gap; each moment of clear attention is a well-placed tile.