The eternal soul forgets its past through ignorance and suffers eternally until awakening through Krishna consciousness.Listen — Srila Prabhupada Uvaca
Pradyumna: ...te vāsudevāya. 6.1.49. [leads chanting, etc.] yathājñas tamasā yukta upāste vyaktam eva hi na veda pūrvam aparaṁ naṣṭa-janma-smṛtis tathā [SB 6.1.49] [01:54] Translation: "As a sleeping person acts according to the body manifested in his dreams and accepts it to be himself, so one identifies with his present body, which he acquired because of his past religious or irreligious actions, and is unable to know his past or future lives." [break]
Prabhupāda: yathājñas tamasā yukta upāste vyaktam eva hi na veda pūrvam aparaṁ naṣṭa-janma-smṛtis tathā [SB 6.1.49] So ignorance, a very good example is given here, that in dream we forget everything, that "I am Mr. Such-and-such, I am inhabitant of such and such place"—everything forgotten. And again when we are awakened, we forget about this dream. This is our daily experience.
But in my awakening stage or dreaming stage, I am seeing both the activities. In the dream, I am the seer, and so-called awake, I am the seer. So I, the spirit soul, experiencing, I remain the same, but circumstances change. Similarly, in our previous birth, what I was, what you were, we cannot remember.
Similarly, you do not know what you are going to become next. But it is a fact that I am, as spirit soul, I am eternal, present. I was present in the past, I am present in the present time, and I'll continue to be present in future. That is explained in Bhagavad-gītā, that "Arjuna, yourself, Myself, and all these persons who have assembled in this battlefield, all of us, we were existing before, we are existing now, and we shall continue to exist." Na hanyate hanyamāne śarīre [Bg 2.20]. This is the first, preliminary knowledge of understanding spiritual life, that "I am eternal." Na jāyate na mriyate vā kadācin.
As spirit soul, I do not take birth, neither I do die. Na hanyate hanyamāne śarīre. I am not finished with the destruction of this material body. That is going on already.
My childhood body is destroyed now. You cannot find out where is that body. My youthhood body, that is destroyed. We cannot find out anymore.
So in this way, this body will be also destroyed, and we shall get another body. Tathā dehāntara-prāptir dhīras tatra na muhyati [Bg 2.13]. In this way we are changing body, one after another. So why there are different types of body? That means the living entity, spirit soul, he is contacting different types of material modes of nature.