本文要處理的問題是：一貫道〈道之宗旨〉講的「大同世界」是不是就是《皇母訓子十誡》裡講的理想世界？在大同世界之上還另有一個太和世界嗎？「大同世界」與超越界的理天又有什麼關係？本文首先對比《禮記．禮運》中「大同」與「小康」的差異，來展示《禮記．禮運》之大同世界的特徵，以作為本文的論述基礎。進而依據《禮記．禮運》之大同世界的特徵來論證一貫道大同思想與《禮記．禮運》之大同思想相通。再來，本文要展示一貫道思想中的大同世界與理想世界，並論證一貫道〈道之宗旨〉所冀望的大同世界就是《皇母訓子十誡》裡的理想人間，而且這樣的世界不只具有「大同」的特徵，還具有《易經．乾卦彖傳》思想中的「太和」特徵，所以一貫道所嚮往的大同世界其實也是太和世界。《皇母訓子十誡》裡的理想世界有兩種，即超越界的理天與理天化的人間，理天是眾生的家鄉，回到理天就是「返本」，就能解脫輪迴。而回到理天的方法就必須要實踐人之本性，這是生命實踐的「返本」。人人都實現本性，人間就能理天化，理天化的人間就是一貫道所嚮往的大同世界、太和世界。

The problem to be dealt with in this paper is: Is the ＂＂Ta Tung＂ World＂ mentioned in the I-Kuan Tao's ＂Tao's Purpose＂ consistent with the ideal world mentioned in ＂Supreme God's Ten Commandments for Children＂? Does the ＂＂Tai he＂ World＂ with a higher level than the ＂＂Ta Tung＂ World＂ exist? And what is the relationship between ＂＂Ta Tung＂ World＂ and ＂Lii Tian＂? This article first compares the difference between the ＂Ta Tung＂ thought and the ＂Xiao kang＂ thought in ＂The Book of Rites＂, and then uses the characteristics of the ＂＂Ta Tung＂ World＂ mentioned in ＂The Book of Rites＂ as the basis of this article. Then, according to the characteristics of the ＂＂Ta Tung＂ World＂ in ＂The Book of Rites＂, it is explained that the ＂Ta Tung＂ thought of the I-Kuan Tao is connected with the ＂Ta Tung＂ thought of ＂The Book of Rites＂. Then, this article will show the doctrine of I-Kuan Tao: the world of ＂Ta Tung＂ and the ideal world. And to argue that the ＂＂Ta Tung＂ World＂ mentioned in the ＂Tao's Purpose＂ is the ideal human world mentioned in ＂Supreme God's Ten Commandments for Children＂. Moreover, such a world not only has the characteristics of ＂Ta Tung＂, but also has the ＂Tai he＂ characteristics mentioned in ＂The Book of Changes＂. Therefore, the ＂＂Ta Tung＂ World＂ in the doctrine of I-Kuan Tao is actually ＂＂Tai he＂ World＂. There are two kinds of ideal worlds mentioned in ＂Supreme God's Ten Commandments for Children＂: The World of ＂Lii Tian＂ and The Ideal Human World. The World of ＂Lii Tian＂ is the home of all species. Going back to ＂Lii Tian＂ is to return to the roots and be able to get rid of the cycle. In order to return to the world of ＂Lii Tian＂, we must practice the moral will of human beings. This is the self-realization of life. If everyone can achieve self-realization, the world becomes an ideal human world. This ideal human world is the ＂＂Ta Tung＂ World＂ that ＂I-Kuan Tao＂ is longing for, and it is also the ＂＂Tai he＂ World＂ that ＂I-Kuan Tao＂ yearns for.