Lin Chi uses a fly swatter and shouting to reinforce the teaching of “The Way”. He tries to show his students physically and mentally how to reach Dharma. Physically striking them as the enemies of Dharma enter their minds, he shows that pride, thoughts, good deeds, evil, hell, heaven are all concepts which take one away from the path. He particularly attacked students that tried to show their own knowledge through questions. This was shown as he spoke to a student about Buddha:

“But even if you open your mouths, what you say will have nothing to do with that concern. Why do I say this? Because Shakyamuni said, did he not, that ‘Dharma is separate from words and writings, and is not involved with direct or indirect causes’” (The Zen Teachings of Lin Chi, Watson b, 1999, p10)

 Lin Chi shows us that thinking about Buddha and the path, are themselves, also enemies of Dharma. That thoughts themselves lead away from Dharma:

“A true student of the way never concerns himself with the Buddha, never concerns himself with bodhisattvas or arhats, never concerns himself with the blessings of the three fold world. Far removed, alone and free, he is never entangled in things. Heaven and Earth could turn upside down and he would not be perturbed.”(The Zen Teachings of Lin Chi, Watson b, 1999, p49)

Just as you cannot touch the surface of a pond, without causing a ripple, Lin Chi shows us that desires, goals, striving, and working hard, to understand Dharma, disrupts the student. Once the pond has been disturbed, it is impossible to see its depths. So Lin Chi describes thoughts and the process of finding Dharma:

“Followers of the Way, if you want to achieve Buddhahood then don’t chase around after the ten thousand things. When mind arises, various kinds of things arise; when mind is extinguished; the various things are extinguished. If only the mind does not arise, then the ten thousand things will be blameless.”(The Zen Teachings of Lin Chi, Watson b, 1999, p73)

Summing up:

 Lin Chi uses physical attacks and shouting to show the path to the Way. Striking students who are thinking of an answer while they pause in thought, or speak with thought, he is showing us that thinking of Dharma and Buddha will never lead to Dharma. That desire, ego, heaven, hell, and all thoughts lead us away from the moment. That this thinking ensures one cannot reach Dharma. Thus one must kill the Buddha to get around the idea of the Buddha, so he can reach Dharma.