Śaktisandhāne śarīrotpattiḥ शक्तिसन्धाने शरीरोत्पत्तिः (sūtra 19)
Śaktisandhāne – śakti + sandhāne – Upon uniting (sandhān means uniting) his willpower with his creative energy; śarīrotpattiḥ - śarīra + utpattiḥ - bodies are created. Usage of word utpattiḥ is significant, as it means producing an effect or a result. Here, effect is the union of yogi’s will power with his high level of concentration.
This sūtra says that high level of concentration on the divine power causes manifestation. Thought process of a yogi when energized with supreme consciousness, leads to desired effects. In other words, the thought process of the yogi is energized with his ability to fix his concentration on the desired object and as a result the desired object is manifested. This energy arises out of his act of making a single unit of his will power and concentration.
Willpower referred here is fully endowed with intellect that is beyond the influence of māyā. When one is not able to reach this highest level of concentration, no mantra initiation, no mantra recitation, no yogic technique would be of any use to him. Śiva, as the Creator brings out those not- totally eradicated desires, the impressions of which still remain as vāsana or impressions in the mind of yogi and make them to manifest. This is brought about by equalizing inhalation and exhalation so thatprāna enters suṣumna nādi causing spiritual energisation.
Spanda Kārikā (verse III.2) says that when such energisation happens in the spinal cord, Śiva appears in his dream and reveals those objects that are prayed for.