Śivasaṃhitā 5.235

The completion of the anuṣṭhāna (ritual vow fulfillment) marks the end of the stage of «service to the mantra» (pūrvasevā) and the beginning of the stage where the mantra «serves the practitioner». This directional change is the heart of the puraścaraṇa (ritual preparation) doctrine: first the disciple serves the deity/mantra with rigor and devotion; then the deity/mantra serves the disciple with its powers.

Anuṣṭhāna = fulfillment of a vow or ritual practice (anu = following, ṣṭhāna = from sthā = to stand, to maintain), kṛta = done/completed, dhīmān = the wise one, the good-intelligenced, pūrvasevā = preliminary service (pūrva = prior/previous, sevā = devotional service).

The concept of pūrvasevā implies a reciprocal relationship between the practitioner and the mantra’s energy. In the Śākta tradition, the goddess is said to «sleep» in the mantra until the practitioner awakens her with devotion and practice. Once awakened, the mantra’s śakti acts independently: the practitioner no longer needs to exert effort because the energy moves by itself from its own liberated impulse.