We are the soul, or the conscious life force within our bodies, and we are completely different from our bodies, which are only highly complex machines.

We sit in the heart, the seat of all energies of the body. From there we experience the world through the wired machinery of the body’s senses, as well as through the more subtle energies of mind, intelligence, and ego.

Understanding the difference between body and soul—between matter and spirit—is the beginning of spiritual life and the only basis for true self-realization.

Our body is constantly changing: infancy, childhood, youth, middle age, old age, and finally death. But we, the unchangeable soul, witness this “virtual reality” from within. That’s why, even though our body changes throughout life, we always keep our sense of identity.

Matter is temporary, and spirit is eternal. Therefore we eternal souls are more important than our bodies. To understand this point is real knowledge.

We are by nature eternally happy and full of knowledge. The human body affords us the opportunity to perform spiritual activities that will free us from getting further material bodies, which are by nature full of suffering.

"Those who are seers of the truth have concluded that of the nonexistent [the material body] there is no endurance and of the eternal [the soul] there is no change. This they have concluded by studying the nature of both." —Sri Krishna, Bhagavad-gita 2.16

More on this topic in Bodies and Souls

http://www.krishna.com/are-we-body-or-soul