The ultimate purpose is to overcome the limitation of mind and go beyond the conceptual realm. This movement inevitably arises from the force of Yoga in living practice. To call Christian Mysticism and Islamic Sufism as Yoga is misleading, because it implies that Yoga is merely some form of practice that could be crafted on to Christianity or Islam. It has adopted the least significant parts of Yoga. Most people don't even meditate.
Yoga is practiced as a very bodily oriented system.
Hatha-Yogic procedures are used as physical therapies. I do not want to take these away from the practitioners. But they do not constitute the essence of Yoga. Yes, it can and has been used for mental health, emotional maturity and fulfillment. A qualified aspirant, eager to engage Yoga, must have clarity of understanding and peace.