Chih-I portrays the Ultimate Truth by equating it with empty space in a house. Empty space in a house has neither roof beams nor pillars. The substance of a house, empty space, thus represents the Ultimate Truth. On the other hand, the roof beams and pillars are taken to analogize the cause and effect of Buddhahood. This is because if a house has no void, it cannot contain and receive anything. If the cause and effect of Buddhahood are not based on the Ultimate Truth as substance, they cannot sustain themselves. Thus, Chih-i holds that it is necessary to single out the correct substance that consists of only one empty space, upon which everything is able to function. (Vol. 2, Page 407-408)

The etymological meaning of the Sanskrit term sūtra refers to vertical threads of a textile or vertical, and such meaning is extended by Buddhists to refer to scriptures that record the teaching of the Buddha. Thus, sūtra can mean line, string, scripture, or the verse or sentences, which convey the teachings of the Buddha, or one of the twelve divisions of scripture. When sūtra is transcribed as Hsiu-to-luo or translated into Chinese Ching, it refers to the scriptures that convey the Buddha’s teaching: in a narrow sense, one of the twelve literary styles of the Buddhist canon; in a broad sense, one of the Tripiṭaka, i.e., the whole scripture. In line with the meanings such as vertical, line, string, sūtra is translated into Chinese as Ch’i-ching, meaning “to conform to,” which is traditionally understood as suggesting that the Buddha ‘s teaching conforms to the truth and is suitable for all people. Ch’i is traditionally interpreted as that which penetrates and embraces. Sūtras are thought to penetrate into the truth and embrace all sentient beings. … According to these various meanings of the word sūtra, Chih-i summarizes five meanings in view of the sūtra being untranslatable (e.g. foundation, slight emanation, gushing spring, line marker, garlands being tied together) and five meanings in view of the sūtra being translatable (e.g. Ching, tallying with, foundation, thread, and wholesome teaching). (Vol. 2, Page 403)

In Chih-i’s system, various types of the Buddha’s teaching are arranged in an ascending order, so that beings can be led to receive the final teaching of the Buddha. To Chih-i, the final teaching of the Buddha should express the most profound doctrine, and the Origin in which the eternal Buddha abides can be regarded precisely as such a doctrine, whereby the Lotus Sūtra is legitimized to be the final teaching of the Buddha. (Vol. 2, Page 402)

For Chih-i, Buddhism consists of the cause and effect of Buddhahood. Looking at the cause and effect separately, the cause of Buddhahood concerns the Buddha’s self-cultivation of striving for Buddhahood, and the effect of Buddhahood concerns the Buddha’s activity of transforming others as the result of his attainment of Buddhahood. Hence, the Origin is considered by Chih-i as the cause of Buddhahood, and the Traces the effect of Buddhahood. However, Chih-i emphasizes that true reality is of no distinction between cause and effect. The cause and effect are contained in each other. The cause decides the realization of effect, and the effect is the manifestation of the cause. Since cause and effect are identical, the cause and effect of Buddhahood are complete in both the Origin and the Traces. (Vol. 2, Page 400-401)

Contemplating mind by going through dharmas (Lei Li-fa Wei-kuan)
Sūtra that is explained by going through dharmas can be approached by contemplating mind. How is this mind contemplation accomplished? This is to identify two opposite aspects as one identical entity, which is of no-distinction of neither this nor that. To be specific, Chih-i points out that if a Mahāyānist contemplates his mind, he contemplates evil mind as being non-evil mind. This means that evil is identical to good and is also neither evil nor good. He contemplates wholesome mind as being non-wholesome mind. This means that non-wholesome is identified with evil and is also neither wholesome nor evil. He contemplates one mind being identical to three minds (i.e., Emptiness, the Provisional Existence, and the Middle Way). With these three kinds of mind that embrace all dharmas, he experiences all minds and all dharmas. In other words, all dharmas are contained in one mind, and mind reflects the true reality that consists of three aspects (Emptiness, the Provisionality, and the Middle Way). One and three is identical to each other, given that three aspects describe one true reality, and one reality consists of three aspects. Such a way of contemplating mind is the foundation for all words, principle and practices. By contemplating mind, each of the meanings sūtra contains can all be embraced by the mind. (Vol. 2, Page 399)

Chih-i illustrates the five meanings of sūtra (in the view concerning the word sūtra as translatable) with reference to the mind contemplation. …
In terms of the mind that is related to the meaning “wholesome teaching”, this means that mind can be taken as the teaching of wholesome words. Mind can also be taken as the teaching of wholesome practice, and wholesome principle. Thus, mind can be extended to contain the meaning track, constancy, and facts.

1. In terms of the mind as track, Chih-i explicates that if there is no contemplation, there is no rule to follow. Because of correct contemplation, mind is in charge. Because of the mind that is correctly in charge, the intention in the mind is also correct, so are practice and principle. If the mind that is in charge tallies with the principle, the intention also tallies with the principle. Therefore, mind can be regarded as track.
2. In terms of the mind as constancy, Chih-i explains that the nature of mind is constantly in concentration, which is like empty space. Such empty space cannot be ruined. Evil consciousness cannot ruin wholesome consciousness, deviant deeds cannot hinder correct deeds, and deviant principle cannot break correct principle. Therefore, mind is regarded as constancy.
3. In terms of the mind as facts, Chih-i explains that everything directing at the mind is taken as contemplation. The accomplishment of the contemplation of wisdom is not in contradistinction to the facts. This is like the fire that aids firewood: the facts and principle are not apart. Written language is contained in nonwritten language. One does not abandon written language in order to contemplate one’s mind. (Vol. 2, Page 398-399)

Chih-i illustrates the five meanings of sūtra (in the view concerning the word sūtra as translatable) with reference to the mind contemplation. …

In terms of the mind as warp and weft that is related to words, Chih-i views the realization as warp, and contemplation weft. This weaves and forms words and speeches. In terms of mind as warp that is related to practice, Chih-i states that the mind that contains the practice of wisdom is taken as warp, and the mind that contains the practice of eliminating defilement as weft. This weaves and forms all practices. In terms of mind as warp that is related to principle, Chih-i holds that the mind, which is vertically in accordance with the principle, is taken as warp, and the mind, which is horizontally in accordance with the principle, as weft. This weaves and forms the doctrine as principle. (Vol. 2, Page 398)

Chih-i illustrates the five meanings of sūtra (in the view concerning the word sūtra as translatable) with reference to the mind contemplation. Each of these five meanings is also scrutinized by Chih-i in terms of words, practice and principle. This is because all speeches and words are caused by mental function; all practices are caused by the mind of thinking; and all doctrines and principles are derived from the mind of wisdom. (Vol. 2, Page 398)

In terms of the mind that is related to the meaning “tallying with,” this refers to the mind that is identical to tallying with the contemplation as wisdom. Tallying with the mind that contains objects as truth is taken as tallying with conditions in terms of suiting the abilities of beings. Tallying with the mind of pleasure and desires is taken as tallying with the teaching as expedient means. Tallying with the mind that contains the Siddhānta for Each Person and the Siddhānta of Counteraction is taken as tallying with practice. Tallying with the mind that contains the Siddhānta of the Supreme Truth is taken as tallying with principle. (Vol. 2, Page 398)

Five meanings that are related to mind are enumerated by Chih-i. …

With regard to the mind that contains the meaning “line marker” (Hsin-shih Sheng-mo), this refers to the mind that is correct without deviance, which is illustrated by Chih-i in reference to words, practice and principle. In terms of the mind that is related to words, this means that by contemplating mind, one is able to obtain correct words, and be removed from deviant words. In terms of the mind that is related to practice, this means that by contemplating mind, one is able to obtain correct thought and eliminate evil actions. In terms of the mind that is related to principle, this means that by contemplating mind, one’s correct mind is able to depart from false views and attachments, and to penetrate the correct principle. (Vol. 2, Page 397-398)