The living being is the marginal energy of the Absolute Personality of Godhead, and he can spend his conserved energy either externally or internally. When spent internally, the energy is identified with the internal energy of the Personality of Godhead, but the same conserved energy, when spent for His external energy, is identified with that external energy. All energies—internal, external, and marginal—are emanations from Him, the Supreme, and they act differently to prove diversity in unity. The unity is the Lord, and the energies represent diversity. The Lord is so powerful that He can do anything and everything merely by His sweet will alone. As mentioned above, everything is done by His energies in a natural way, with full knowledge and complete perfection. That is the information we have from the Vedic literatures.
The internal energy and the marginal energy are of the same superior quality, but the external energy is inferior in quality. That is the information we have from Bhagavad-gītā. Because the living entity is classified as marginal energy and is of the same quality as the internal energy, it is quite natural for him to cooperate with the internal energy. But when the living entity prefers to cooperate with the external energy, he is put into difficulty. By the process called pratyāhāra (diversion), yoga diverts our energies from the external to the internal.
The energy of our senses is meant to be diverted, not stopped. The senses are to be purified, so that they serve the Lord instead of disturbing His settled harmony. The entire cosmic harmony is a settled fact by the will of the Supreme. So we must find the supreme will in every action of the cosmic situation. That is the instruction of Īśopaniṣad. The human life is an opportunity to understand this cosmic harmony, and therefore our conserved energy, which is likened to the conserved water in the paddy field, must be used for this purpose only.
As there is no chance of rain from the sky in autumn, we shall not immediately have a chance to get a human body again if we spend our conserved energy for sense enjoyment. The senses have their utility for the service of the Lord, and if properly engaged they can reach the highest perfection by being directly engaged in the service of the Lord in His personal presence. When the living entity thus goes back home, back to Godhead, and engages in the personal service of the Lord, he is said to have attained saṁsiddhi paramā, the highest perfection. This is confirmed in Bhagavad-gītā.