Sri Aurobindo translates Shwetashwatara Upanishad, Chapter Six, Verse 21: “By the might of his devotion and the grace of God in his being, (Or, By the grace of the Lord, by the energy of his askesis,) Shwetashwatara hereafter knew the Eternal and he came to the renouncers of the worldly life and truly declared unto them the Most High and Pure God, to whom the companies of seers resort forever.”
As we see in a number of Upanishads, the power of tapasya is considered essential. Concentration of will in the thought, one-pointed devotion to the seeking, is necessary preparation for the seeker to loosen the hold that external perceptions and events have on him, so that he can be ready and receptive for the response from the Divine, the Grace of God, to provide the illumination. This triple process Sri Aurobindo describes in The Mother as one of aspiration, rejection and surrender. The resultant receptivity in the being is the opening needed for the Grace to respond.
The seeker cannot command the Grace. The seeker can only create the conditions within which the Grace can act if it so chooses. When the seeker obtains the realisation, he becomes capable of communicating the process and the necessary pre-conditions to others who have similarly prepared themselves by renouncing attachment to the outer life of the world.
The question of renunciation of the worldly life is one that is subject to interpretation. Ascetic paths ask the seeker to entirely abandon all actions in the world, other than those specifically necessary for basic survival and the inner focus needed for the realisation. Others, including the Bhagavad Gita, define this renunciation as overcoming attachment to the objects of desire in the world. The Taittiriya Upanishad refers to those “whose soul the blight of desire touches not.” For those who achieve the knowledge by identity with the Eternal, there is a liberation from the bondage but a continuation of the participation in the manifestation.
Sri Aurobindo, The Upanishads, Shwetashwatara Upanishad, pp.369-384