According this definition of Patanjali central point in yoga is to develop Ekagrata.
Ekagrata or one pointed mind indicates the ability of the yogi to concentrate on one object, and to maintain continuous concentration without allowing any kind of distraction to disturb his concentration.
The object of concentration can be anything like physical object, image of a deity, the point between the eyebrows,it can be a thought, metaphysical idea or God.
So how do we achieve this?
-we achieve this with the control of prana (pranayama)
And how do we control the prana?
-we control the prana or the energy with controlled and conscious breathing.
The breathing is the most essential part of yoga. You can do numerous yoga practices today in almost every fitness center or gym but if you do not pay attention to your breathing, or if you do not breath properly than you are not doing yoga, you are just stretching.
Patanjali in his Yoga Sutras presents a systematical approach of physiological and spiritual exercises grouped in eight categories called Ashtanga yoga. This system enables us to develop ekagrata and eventually achieve Samadhi ( knowledge of our true nature or enlightenment) which is the ultimate goal of yoga.