Three Thousand Realms (or Worlds) In a Momentary Existence of Life
Each of the Ten Realms [Hell, Hunger, Animality, Anger, Humanity, Rapture, Learning, Self Realization, Bodhisattva, and Buddha], one of which is manifest from moment to moment, contains Ten Realms which are latent, thus making One Hundred Realms. Each of the One Hundred Realm contains the Ten Factors, thus making One Thousand Realms. Each Realm also contains the Three Principles of Individuation [the Realm of the Individual, the Realm of the Society of Beings in which the individual resides, and the Realm of the Environment in which the individual resides] thus making Three Thousand Realms.
In general, a Bodhisattva [selfless being] manifests primarily Bodhisattva from moment to moment and always quickly returns to Bodhisattva when manifesting one of the other realms. The Bodhisattva has the Appearance, Nature, Entity, Power, Influence, Cause, Condition, Latent Effect, Manifest Effect, and Consistency from Beginning to End of a Bodhisattva. Both the society or collection of beings in which the Bodhisattva resides and the environment [land] of the Bodhisattva manifest predominantly the Realm of Bodhisattva.
In general, a cat manifests primarily Animality from moment to moment and always quickly returns to Animality when manifesting one of the other realms. The cat has the Appearance, Nature, Entity, Power, Influence, Cause, Condition, Latent Effect, Manifest Effect, and Consistancy from Beginning to End of an animal. Both the society or collection of beings in which the cat resides and the environment of the cat manifest predominantly the Realm of Animality.
A Bodhisattva will manifest Animality for periods of time when, for example, he experiences the urge to sleep or defecate.
A cat will manifest Bodhisattva for periods of time when, for example, it acts selflessly towards its kittens or its owner.
Tientai asserted that every being has the potential to elevate its central life tendency [or the Realm or Realms to which it gravites] through the principle of Ichinen Sanzen. For example, a cat can create the causes and conditions for Bodhisattva by either very strongly [for a moment] or habitually acting selflessly. Intent, according to Tientai, is far less important than actuality or suchness in elevating [or lowering] one's central life tendency.
The practice advocated by Tientai was meditation directed towards perceiving the Three Thousand Realms In a Momentary Existence of Life. He recited the title of the Lotus Sutra ten thousand times a day for his personal practice but since the time and the people's capacity were not ripe for the widespread propagation of the principle practice of the Lotus Sutra, he refrained from advocating this practice for others.
Nichiren Daishonin taught Actual Ichinen Sanzen or one moment of exceptionally profound faith and joy in Namu Myoho renge kyo and its continuous recollection is itself Buddhahood.