Our true nature never, automatically, reveals itself to us because it is thoroughly incorporeal. Still, it is never non-present. Accordingly, this incorporeality is ungraspable by the corporeal senses including even our consciousness which we cling to, tenaciously.
When we learn, for the first time, of our true nature from the teachings of the Buddha it seems dark and hidden from us since we are trying to see it as something corporeal which is all that we know. The corporeal, we don't realize, is continually obscuring our true nature, as it were, hiding it from us almost completely. It seems for us that a dark veil covers our true nature which we can't rend.
Naturally, when our true nature is revealed, which is luminous and compassionate, only then is the darkness dispelled. When it is not taken away we seem doomed to suffering and death; we see no means of escape. In fact, the idea of the luminous seems alien to us. In this regard, there seems to be two opposed worlds, the world of light and the world of darkness, or the same, the world of unconditionality (nirvana) and the world of conditionality (samsara). But from the awakened standpoint it is one substance that expresses itself as an arising and a return, this really being the arising of infinite power/compassion and a return to self-knowingness.
The unawakened, on the other hand, are only aware of birth and death because of their strong attraction to the corporeal. In this condition, will or desire can dangerously exalt itself which then becomes entrapped in the cycle of birth and death with no way out. This is really regression led by a will to more and more corporeal states. Such a person who exalts their will is an icchantika.
"Also, next, O good man! For example, a burnt seed will not call forth buds, even if the rain falls on it for a period of 100 thousand million kalpas. There can never be a situation in which this seed will bring forth buds. The same with the icchantika. No bud of Enlightenment springs forth, even if the icchantika gives ear to this all-wonderful Great Nirvana Sutra. Such can never happen. Why not? Because such a person has totally annihilated the root of good. As with the burnt seed, no root or bud of Bodhichitta will shoot forth" (Mahayana Mahaparinirvana Sutra).