Transformation of potential energy of soul into dynamic one, which occurs on account of the Kṣayopaśama (annihilation-cum-subsidence) or Kṣaya (annihilation) of the Vīryāntarāya (Karma, obstructing the spiritual energy) and the Udaya (rise) of Śarīranāma Karma (sub-type of body-making Karma, responsible for appropriation and coalescing of corresponding material clusters).
vīryāntarāyakṣayakṣayopaśamato...labdhivīryakāryabhūtā kriyā karaṇaṃ tadrūpaṃ karanavīryam.
(Bhaga 1.376 Vṛ)