A sattwic tapasya is characterized by balance and harmony, as well as appropriate control over body, speech and mind. Sattwic tapasya prepares the nature for its evolutionary advancement, focuses and purifies the energies, and helps liberate the soul from the bondage of the lower nature.
Sri Aurobindo describes the Gita’s view of sattwic tapasya: “First comes the physical, the askesis of the outward act; under this head are especially mentioned worship and reverence of those deserving reverence, cleanness of the person, the action and the life, candid dealing, sexual purity and avoidance of killing and injury to others. Next is askesis of speech, and that consists in the study of Scripture, kind, true and beneficent speech and a careful avoidance of words that may cause fear, sorrow and trouble to others. Finally, there is the askesis of mental and moral perfection, and that means the purifying of the whole temperament, gentleness and a clear and calm gladness of mind, self-control and silence. Here comes in all that quiets or disciplines the rajasic and egoistic nature and all that replaces it by the happy and tranquil principle of good and virtue.”
As the sattwic tapasya progresses it begins to transcend its roots in the Gunas and bring about an increasing identity with the Divine spirit and presence which finds a suitable foundation in the nature prepared by this discipline. “And what will remain then will be the spirit’s immaculate Tapas, a highest will and luminous force in all the members, acting in a wide and solid calm and a deep and pure spiritual delight, Ananda. There will then be no farther need of askesis, no Tapasya, because all is naturally and easily divine, all is that Tapas. There will be no separate labour of the lower energism, because the energy of Prakriti will have found its true source and base in the transcendent will of the Purushottama. Then, because of this high initiation, the acts of this energy on the lower planes also will proceed naturally and spontaneously from an innate perfect will and by an inherent perfect guidance. There will be no limitation by any of the present Dharmas; for there will be a free action far above the rajasic and tamasic nature, but also far beyond the too careful and narrow limits of the sattwic rule of action.”
Sri Aurobindo, Essays on the Gita, Second Series, Part II, Chapter 18, The Gunas, Faith and Works, pp. 472-473