Based on Chapter 48, what is the ultimate key to controlling the senses and achieving liberation?

The ultimate key to spiritual progress, as detailed in Chapter 48, is unwavering faith (Bhava). This faith is the very cause for crossing the ocean of worldly existence. From this faith arises uninterrupted love, and where there is love, devotion, peace, and detachment reside. Liberation is said to stand right behind a heart full of devotion. The practical application of this principle is that by serving Sai Baba's feet with this devotional spirit and constantly remembering him, the senses will cease to behave erratically. This control over the senses makes the difficult journey across the ocean of existence easy and certain, leading one toward the ultimate goal of liberation.