Spiritual realization is difficult for person asadbhiḥ. Why it is difficult? Viṣayātmabhiḥ. Because they are simply attracted by the four principles of material life: eating, sleeping, sex life and, one day, death. They cannot. One must be above this interest. One must be very sane man, that "These kinds of interests are there in the animals. So if I am also interested in only these things, then where is the difference between this dog and me?" Something more.
That information is given in the Bhagavad-gītā: avināśi tu tad viddhi yena sarvam idaṁ tatam (BG 2.17). Yena sarvam idam. This body is perishable, asat. But there is another sat, means permanent thing. What is that? Avināśi tu tad viddhi. You try to understand that thing which is eternal. What is that? Yena sarvam idaṁ tatam, that which is spreading all over your body. You pinch your body, you feel pain. Why? Because there is consciousness. Therefore consciousness is permanent. And as soon as the consciousness is gone, you chopped up your hand, no response. So that . . . it is a very nice statement. Tat, that consciousness, is avināśi, is eternal. Where is the difficulty?