Several Concepts in Zen Buddhism
The original meaning of Pure Land refers to the Buddha-land, where there is no evil destiny, and all beings are almost but not quite destined for nirvana. Nowadays, Pure Land more often refers to the teaching of Pure Land Buddhism. In China:
“Pure Land (Ching-te) – the practice aimed at gaining rebirth in Buddha-field – was never a formal school or lineage in China. … However, from the sixth to the ninth century a string of teachers specializing in Pure Land practice, and offering a specifically Pure Land doctrine, …… laid the groundwork for the Pure Land school of Japan.”
In Japan, Pure Land movement was pressed by the signs of mappo, when people are unable to realize salvation on their own. Pure Land schools thus calls for the help of Amita. There are Jōdo-shū (Pure Land sect) and Jōdo-shin-shū (True Pure Land sect), one focus on the repetition of practice, and the other on the purity of intentionality.
However, to view Pure Land literally as the Buddha-land is not the Buddha’s way. Since everything is Buddha, Buddha-land is own-land, that is, the context of your awareness. Implying the doctrine of Emptiness, there is no self except in the construct of the relation to “others”, and therefore there is no Pure Land except in the construct in relation the world. To born in Pure Land, is to interact and to open awareness.
In Japanese Buddhism, Mappō refers to the age of Degeneration or the End of Dharma, which consists not only the absence of progression, but also the incapacity to commit to one’s gifts, the Buddha nature. In thirteenth-century Japan,
Belief was widespread that Buddhism had reached the final and most decadent period of the Buddha’s teaching, the period called Mappō, “the end of the Dharma,” when enlightenment, especially by one’s own efforts, would be more or less impossible.
Such belief pressed Buddhism into certain changes, including the formation of three major popular Pure Land schools and Nichiren-shū. In respond to Mappō, Pure Land Buddhism seek help from Amia. Different from them, the solution Nichiren-shū provides is to annihilate the false Dharma, believed to be the reason of Mappō, and to “bring the entire nation to the worship of the truth as contained in the Lotus Sutra.”
Some say Mappō is right now: endless environmental and political disasters, and ubiquitous distractions from commitment. Does Mappō really exist, and when did or shall it come? Since everything is transient, and so should Mappō be. Thus, in the karmic world, Mappō is always here in the moment, and is always yet to come. It is the inescapable suffering, every thwart to attainment of enlightenment. On the other hand, since nothing is static, how could Dharma come to an end. Symbolically, Mappō calls on the urgency to practice, to regain the capacity to self-realization.
Nembutsu is the recitation of the name of Buddha Amida. In early time, it functioned
as “a means of gaining merit devoted to the attainment of nirvana” in Tendai system. Later as the belief in Mappō pervaded, nembutsu soon became the hallmark Japanese Pure Land practice, calling for the salvific power of Amida.
Two interdependent questions emerge: does nembutsu ultimately depend on “other power” or “own power”; is it a matter of quantity or quality?
Hōnen, founder of Jōdo-shū school primarizes the times of the practice, and pointed out the importance to think about Amida instead of the self at all time. Intentionality is secondary since repetition shall either leads the construction of mind, or the result which really matters.
On the other hand, Shinran, the inspiration of the Jōdo-shin-shū believes that “the saving grace of Amida required only one nembutsu.” He asserts that the only thing that matters is the purity of one’s intention and underlined the true nature of Amida as an embodiment of Tathāgata, which by nature is jinen honi, or “that which becomes such on its own”. However, since the purity of intention requires abandonment of all sense of jiriki (self-power), Tathāgata can only be experienced as something totally other. In this way, the intention becomes the practice itself, and the practice is the intention. 
“Zazen practice is the direct expression of our true nature.”
In Zen Buddhism, zazen is the primary meditative discipline, meaning “seated meditation”.
Zazen is the practice of beginner’s mind, which is empty and open to everything. It The practice of zazen consists of the right practice, the right attitude, and right understanding.
The right practice is not equivalent to the right posture, though according to Suzuki “the state of mind that exists when you sit in the right posture is, itself, enlightenment.” Nonetheless, the “essence” of right practice is to own your own body and mind with effort, and find perfect calmness in them. In this sense, the “right posture” is not limited to the cross-leg sitting position.
The right attitude of zazen is to concentrate without trace, and to repeat with no gaining idea, no attachment to the attainment. The quality of zazen shall express itself through beginner’s mind, but the practice has no self, no goal or intention. In a sense, to practice zazen is no practice, since it traces back to the Tendai doctrine stating all human beings already have Dharma-nature. Thus, nonthinking in zazen is dethingking, or deconstructing, involving thoroughly investigate perception, intention, and consciousness. 
The right understanding of zazen is Buddha nature, that is empty. True understanding is no understanding, an openness to any understanding. It evolves in practice and turn back into practice, and thus the actual practice itself.
The literal translation of Koan is “public cases”, in Japanese Zen Buddhism, it is assigned to meditator by roshi as a central topic of meditation, either to provide an object to concentrate, or to deliberately subvert one’s logical sense and attached point of view, and forces him or her into further understanding of the world.
Koan is inseparable from the practice of zazen, only to those who have certain experience with zazen would be assigned koan to investigate. They further mutually reinforce each other.
Generally speaking, a koan brings about awakening more quickly than other types of practice because it provides a tool for focusing one’s efforts.
Koan training is sometimes viewed as too harsh, using encouragement stick by roshi. However, it is only used under one’s own will, and it is a will of suffering. The will of suffering lies in the Four Nobel truth, as it is in suffer that suffer accesses.
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 The Experience of Buddhism, p. 332
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 Buddhist Religions, p. 253-254
 Zen Mind, Beginner’s Mind, p. 29
 Zen Mind, Beginner’s Mind, p. 23
 Zen Mind, Beginner’s Mind, p. 28
 Zen Mind, Beginner’s Mind, p. 39
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 Zen Mind, Beginner’s Mind, p. 97
 Zen Tradition and Transition, p. 56