The external energy, composed of pradhana or prakrti as the ingredient-supplying portion and maya as the causal portion, is known as maya-sakti. Inert material nature is not the actual cause of the material manifestation, for Karanarnavasayi, Maha-Visnu, the plenary expansion of Krsna, activates all the ingredients. It is in this way that material nature has the power to supply the ingredients. The example given is that iron has no power to heat or burn, but after coming in contact with fire the iron becomes red-hot and can then diffuse heat and burn other things. Material nature is like iron, for it has no independence to act without the touch of Visnu, who is compared to fire. Lord Visnu activates material nature by the power of His glance, and then the ironlike material nature becomes a material-supplying agent just as iron made red-hot becomes a burning agent. Material nature cannot independently become an agent for supplying the material ingredients. This is more clearly explained by Sri Kapiladeva, an incarnation of Godhead, in Srimad-Bhagavatam (3.28.40):

"Although smoke, flaming wood, and sparks are all considered together as ingredients of a fire, the flaming wood is nevertheless different from the fire, and the smoke is different from the flaming wood." The material elements (earth, water, fire, etc.) are like smoke, the living entities are like sparks, and material nature as pradhana is like the flaming wood. But all of them together are recipients of power from the Supreme Personality of Godhead and are thus able to manifest their individual capacities. In other words, the Supreme Personality of Godhead is the origin of all manifestations. Material nature can supply only when it is activated by the glance of the Supreme Personality of Godhead.