Tatra sthitau yatno abhyasa
Sthitau: Stability in the two
The persistent effort of a sadhak to stabilize him/herself in the twin instruments of abhyasa (practice) and vairagya (detachment) to achieve the final frontier has been termed as 'abhyasa' by Sage Patanjali.
Yoga is a practical science, there is no theory. Till and unless the sadhak practices the various tenets and gains their gyan through experience under a Guru, yoga will remain a bookish exercise. The situation maybe compared to playing the best music in the world to a person whose ears are plugged or presenting the best scenery in the world to a blindfolded man. Practice is a must, else you will miss out on the essence of the subject. The experience will evade you, as will the glow. Guru can show you the path and put you on it, but the effort to walk that path, abhyasa, has to be your own.