The history of yoga is based in the Indus Valley civilization.
The techniques are practiced by the Indus to initiate spiritual growth. The yogis encourage union with the finite jiva (transitory self) and with the infinite Brahman (eternal self). Brahman is a term used by the Hindus to mean God. So, what are we supposed to unite with? Yogis usually think of God as an impersonal, spiritual substance, coexisting with all of reality.
This doctrine is called pantheism which is the view that everything is God. In the Bible, God reveals Himself as the personal Creator of the universe. Since it is taught by the yogis that everything is God, it then stands to reason, man is God. Christianity, on the other hand, teaches us there is a clear distinction between man and God. Since God is the Creator, we are one of his creations and created in the image of God.
Unlike the yogis, the Bible presents mans primary problem to be sin — a failure to conform to Gods character and standards. The solution is Jesus Christs death on the cross. He calls men to freely receive all the benefits of His salvation through faith in Christ alone.
Yoga views mans problem primarily in terms of ignorance. Man simply does not understand he is God so the solution is enlightenment, or an experience of union with God. In order to reach that goal, there must be a lot of striving and effort which is not needed in the Christian viewpoint.