The Great Concentration and Insight by Grand Master T’ien-t’ai is the greatest of his works and contains the essence of the holy teachings of Śākyamuni Buddha preached in His lifetime. About 500 years or so since Buddhism was brought into China, the wisdom of the three Southern and seven Northern masters was comparable to the sun and moon, and their virtue resounded in the whole world. Yet they were at a loss as to the profundity, comparative superiority, and sequence of His lifetime preaching. It was then that Grand Master T’ien-t’ai not only explained the Buddhism of Śākyamuni Buddha once more but also extracted the wish-fulfilling gem from the storehouse of the five Chinese characters of the Lotus Sūtra entitled “3,000 existences contained in one thought,” giving it to all the people in India, China, and Japan.
This doctrine of the Great Concentration and Insight was explained for the first time in China. Even the commentators in India were unable to explain it. Grand Master Chang-an, therefore states at the beginning of the Great Concentration and Insight, “The clear and modest doctrine of the Great Concentration and Insight had never been heard of,” and the Profound Meaning of the Lotus Sūtra, fascicle 3, declares, “Even the Great Wisdom Discourse by Nāgārjuna in India cannot compare to it.”
In particular, the “3,000 existences contained in one thought” doctrine expounded in the Great Concentration and Insight, fascicle 5, is all the more profound. When we speak of this doctrine, it is inevitable that devil’s will come to hinder us. Put another way, when devils do not come to hinder us, we know the True Dharma is not involved. Therefore, it is stated in the Great Concentration and Insight, fascicle 5, “As practicing and understanding of the ‘tranquility and contemplation’ progress, the ‘three hindrances and four devils’ compete to interfere with the practicer. … Do not follow them or fear them. When one follows them, one will fall into the evil realms; and if one is afraid of them, one will be unable to master the True Dharma.” This is exactly what I have experienced with my own body. Also, this should be a clear mirror for my disciples and followers to reflect upon. Please practice with reverence, thereby producing nourishment for the future practicers of the Lotus Sūtra.
The “three hindrances” in this citation refer to evil passions, evil karma, and painful retributions. The evil passions are the obstacles arising from the three poisons of greed, anger, and stupidity; the evil karma refers to the obstruction arising from wives and children; and the painful retributions are obstructions caused by the rulers of a country, parents, and others. Among the “four devils” that cause hindrances is the king of devils in the Sixth Heaven in the realm of desire.
Kyōdai-shō, A Letter to the Ikegami Brothers, Writings of Nichiren Shōnin, Volume 6, Followers I, Page 83-84