In Sanskrit, the word 'yoga' means 'union.' The goal of the practice of yoga is union with God. Contrary to the Westernized idea of yoga as a matter of body postures and asanas performed mostly for health, the true yoga is a spiritual practice designed to bring the practitioner closer to the great creator of the universe, the ultimate soul, God. This is not to say that asanas and physical well-being are not important. They are. But real yoga is a science and practice of the soul.
The aim of this practice is to calm the mind, close the senses, and open the doors of true soulfulness--true liberation from worldly suffering. According to the yogins of old, the purpose is to--through single-pointed meditation--to close off the senses and deprive them of worldly pleasure so that we go within to find the source of true bliss, true soul. This can only be found through realization of our higher selves--which is the sacred space in the heart that unites us with God.
Through the practice of yoga, I have been able to calm my restless spirit and find peace. This peace is our very nature. It is the peace we were born with and to which we can return in this life--not just in the afterlife. To find it, though, we must still our minds and find the silence within.
As Patanjali tells us in the Yoga Sutras, we will find in this silence the changeless, timeless, deathless source of all true joy--God.