It is this truth which makes necessary to every philosophy of Yoga the conception of the Ishwara, Lord, supreme Soul or supreme Self, towards whom the effort is directed and who gives the illuminating touch and the strength to attain.
Aurobindo argues that Ishwara is a structural necessity in any Yoga philosophy, functioning as the transcendent source of illumination and the ultimate object of the practitioner’s aspiration.
, The Synthesis of Yoga, 1948thesis