What philosophical lesson does Chapter 15 impart regarding the attainment of the Guru's grace through devotion?

The core philosophical lesson in Chapter 15 is that persistent, unwavering devotion can melt the heart of the Guru and secure His grace, even if it seems unrequited at first. The chapter uses the analogy of the kittens and the mother cat to demonstrate this principle. Despite the mother's initial annoyance, the kittens' complete and loving attachment ultimately causes her to forget her irritation and shower them with affection and nourishment. Chapter 15 applies this directly to the spiritual path, suggesting that a devotee's sincere and total attachment to Sai's feet is the very mechanism that makes His heart overflow with love, granting them His vision and helping them achieve the supreme goal, Paramartha.