If you examine the meditation poses depicted in the world's great spiritual traditions, you'll find that they all have one thing in common — the unshakable stability of a mountain or tree. Look at the kneeling pharaohs in the Egyptian pyramids, for example, or the cross-legged Buddhas in Indian caves or Japanese temples. They sit on a broad base that appears to be deeply rooted in the earth, and they have a grounded presence that says, "I can't be budged. I'm here to stay."
When you sit up straight like a mountain or a tree, your body acts as a link between heaven and earth — and by analogy, connects your physical, embodied existence with the sacred or spiritual dimension of being. In addition to the spiritual aspect, you might consider that sitting up straight confers some practical benefits as well. By aligning the spine and opening the channels that run through the center of the body, upright sitting encourages an unimpeded circulation of energy, which, in turn, contributes to wakefulness on all levels — physical, mental, and spiritual. Besides, it's a lot easier to sit still for extended periods of time when your vertebrae are stacked like a pile of bricks, one on top of the other. Otherwise, over time, gravity has this irritating habit of pulling your body down toward the ground — and in the process, causing the aches and pains so typical of a body at war with the forces of nature. So, the most comfortable way to sit in the long run is straight, which puts you in harmony with nature.
Of course, you can always lean against the wall — or so you may think. But your body tends to slouch when it leans, even subtly, in any direction; and the point of doing meditation is to rely on your direct experience, rather than to depend on some outside support to "back you up." When you sit like a mountain or a tree, you're making a statement: "I'm deeply rooted in the earth, yet open to the higher powers of the cosmos — independent, yet inextricably connected to all of life."
Take your position