kṛṣṇa-śaktye - by the energy of Kṛṣṇa; prakṛti - the material nature; haya - becomes; gauṇa - indirect; kāraṇa - cause; agni-śaktye - by the energy of fire; lauha - iron; yaiche - just as; karaye - becomes; jāraṇa - powerful or red-hot.

Thus prakṛti, by the energy of Lord Kṛṣṇa, becomes the secondary cause, just as iron becomes red-hot by the energy of fire.