Pratyahara is situated directly in the middle of the eight limbs, its central position indicates that it is the point where the outer can become inner (and also the reverse).
If yoga is to take its proper place as an main, effective agent for positive change in the world it is because of the philosophy that it is based on—not as much because of the power of doing the physical postures.
Even though most of us begin yoga without giving much or any thought to the yamas eventually we open the door to contemplating and even putting them into action.
To practice Isvara pranidhana is to endeavor to live your life from the perspective that everything under the sun shares a benevolent, invisible, cohesive, inescapable connection with everything else.
Look to this book, study this book, marry this book, obsess over this book, consume this book, love this book, bow to this book, become a connoisseur of this book, appreciate its subtle bouquet, its heady nose, its earthy, chewy flavors...