The ten thousand things each has its merits,
that should be said of their functions and situations.
Phenomena exists like boxes and lids fitting,
with principles, that should be like arrowheads in posts.
Chán Master Shítóu Xīqiān
(Harmony Of The Unequal And Same)
It is a fact, however, that at about this time , many samurai warriors began to practice Zen meditation with Rinzai teachers. The goal-oriented concentration of Rinzai meditation [临济禅] appealed to the samurai, it is said, as a means to reduce fear of death in battle. Even so, one historian wrote, “one does not have to look far in Japanese historical sources to find references to badly wounded samurai chanting, ‘Namu Amida Butsu’ [南无阿弥陀佛] as opposed to focusing on becoming one with their gradual dying on the battlefield.” [Christopher Ives, Imperial-Way Zen: Ichikawa Hakugen’s Critique and Lingering Questions for Buddhist Ethics (Honolulu: University of Hawaii Press, 2009), 104]
‘Namu Amida Butsu’ is the Japanese form of chanting the name of Amitabha Buddha [with profound Faith and sincere Aspiration] to gain rebirth in the Pure Land, [where one transcends the cycle of birth and death, with swiftest and full enlightenment guaranteed]. Some samurai intensely engaged in Rinzai Zen practice, and a few became masters. It appears though that most Zen-practicing samurai sought the mental discipline to be better warriors but were not so keen on the enlightenment part of practice…
[Unfortunately, many extremist] ‘Zen’ teachers [later, circa 1944] [ab]used the teaching of emptiness to justify slaughter, saying that ‘no one’ would be killed… There were arguments that, since nothing has intrinsic self-nature, war itself can be neither good nor bad. A war fought for a justifiable cause is righteous, it was said. This of course begs the question, what cause is so justifiable?…
The closest thing to a ‘just war theory’ in Buddhist scripture is in an obscure Mahayana sutra called the Arya-Bodhisattva-gocara-upayavisaya-vikurvana-nirdesha Sutra… According to this sutra, there is no justification for wars of aggression. If a nation is invaded, a ruler may use arms to defend his kingdom and protect his people, but he may only use as much force as necessary to expel the invaders. Injuring and killing the invaders should be avoided if possible, though it is acknowledged that this may not be possible. Once the invaders are expelled, the ruler is not to pursue and punish them but must try to make peace with them.
The Circle of the Way:
A Concise History of Zen from the Buddha to the Modern World