Sense-withdrawal. Why would we want to withdraw our senses and what exactly does that mean. Pratyahara is the fifth limb and it acts as a sort of bridge between the first four limbs and the last three. We are observing and enhancing our awareness of our behavior, our habits, our physical condition and our breath in the first four limbs and now we need away to turn inward to examine the functioning of our mind, and to surpass the mind and its ego to reach God Consciousness. It is not as simple as just sitting down and counting your breath. If it were that simple, we would all be enlightened by now and could probably get rid of those little purple mats. When we do sit down to observe our breath we are distracted, over and over again. What distracts us? The sounds from outside, the sounds or smell of the person next to us, our grumbling tummy or our sore bottom. Then what? Our mind travels to our thoughts about the person next to us, or to what we may want to eat for lunch after this god-forsaken session is over. Or to whether or not we ought to adjust our sitting position. This is a chain reaction that could go on and on until we catch ourselves so far removed from what we were initially trying to do that we don't even know how we got there! Sense withdrawal begins when we finally become aware of our distractedness. When we are able to catch ourselves moving "outward" with our thoughts and re-direct them back "inward", we are beginning to actually practice sense withdrawal. My teacher likes to make the distinction between the first four limbs and the last four limbs this way: the first four are things we do, or practice; the second four are things that will happen spontaneously after much practice. Pratyahara is that bridge where we can try to practice withdrawing our senses from outside stimuli but which will only truly be mastered when that sense withdrawal begins to happen spontaneously each time we sit to practice pranayama or meditation. In fact, most of the meditation exercises you learn in a class or from a book are really just practicing turning inward so that eventually meditation will happen. We can't make ourselves meditate, we can only encourage the process by withdrawing our senses.
Again, why would we even want to do this? Studying the mind is a good way to learn what we actually give our attention to all day. It is a more advance practice of Yama and Niyama, in that we are taking ourselves further into the realm of the endless chatter of the mind to see what this is really all about and whether or not half of what distracts us is even necessary. We are attempting to become more efficient, to waste less fuel, so to speak. Distraction wastes energy. We want to be in control of what distracts us. Some distractions are necessary and even pleasant. Most are not. Who is in control? The practice of sense withdrawal puts us firmly in control. The spontaneous withdrawal of the senses suggests mastery of our senses while also taking us on a fascinating journey to the inner workings of our mind.