Our Dualistic Nature

When the root of duality--dualistic clinging, dualistic perceptions, deluded perceptions--is severed, all the leaves, the branches, and even the tree trunk of samsara and nirvana naturally wither on their own and topple in their own time. Then this great spreading tree of samsara and nirvana, of duality, of worldliness, of conditioned being, does not need to be chopped down: it is already as if dead. We can relax; done is what had to be done, as the Buddha sang.
This is the whole point of the Dharma, of spiritual awakening, of Buddhahood; this is its ultimate evolution or unfolding. If we aspire to experience such an awakening, there is nothing else to do except recognize the true nature of our primordial awareness, our own essential being, our own birthright, which is within. This is the intrinsic nature of our own heart-mind, also known as bodhicitta or bodhi-mind. It is our own being, our own nature, this renowned buddha-nature. It is not a Buddha anywhere else.
--from Natural Great Perfection: Dzogchen Teachings and Vajra Songs by Nyoshul Khenpo Rinpoche and Lama Surya Das, published by Snow Lion Publications

The Essence of the Four Noble Truths

Shortly after attaining enlightenment under the bodhi tree, the Buddha gave a sermon in Varanasi sharing the fruits of his realization. This sermon is referred to as the "first turning of the wheel of Dharma." The word Dharma here refers to the Buddha's teachings themselves. It was this sermon in which the Buddha developed what would become the framework for the entirety of his teachings: the four noble truths.
These four truths are the truth of suffering, the truth of its origin, the truth of the possibility of its cessation, and the truth of the path that leads to that cessation. In essence, the four noble truths say that we all naturally desire happiness and do not wish to suffer--and that the suffering we wish to avoid comes about as a result of a chain of causes and conditions begun even before our birth. If we are to pursue our aspiration to gain freedom from suffering, we need to clearly understand the causes and conditions that give rise to suffering and strive to eliminate them. Additionally, we must clearly understand the causes and conditions that give rise to happiness as well, and actively practice them. This is the essence of the four noble truths.
--from Essence of the Heart Sutra: The Dalai Lama's Heart of Wisdom Teachings by H.H. the Dalai Lama, translated & edited by Geshe Thupten Jinpa