「一以貫之」蘊含著孔子聖道相傳的心法。然而歷來的文章鮮有深論「一以貫之」的工夫，大都以「忠恕」之「二」來分析「一以貫之」之「一」，而忽略了「一」本身在孔子哲學中之工夫義。本文研究發現「一以貫之」之「一」之工夫內涵可以分為「當下一心」、「人我一體」、「本末一貫」三部分來闡釋。意即可以從時間（當下一心之無間）、空間（物我一體之無外），以及易簡之聖學方法（一心即多聞）等三個維度來詮釋孔子一以貫之的工夫內涵。最後亦推論得知孝弟的親親之愛其實就是堯舜孔孟一貫心法。親親的本身就是「當下一心」、「本末一貫」。落實而言，從親親而「家人一體」，進而可以推致人人親親的「人我一體」，乃至「物我一體」。從成德之教的角度來說，多聞乃為一以貫之而多聞，如是，一貫也即可多聞也。

＂One principle runs through it all＂ is a core mental cultivation method in the teachings of Confucius. However, most articles analyzed it through the dual concepts of loyalty and forgiveness, and the implications of its ＂oneness＂ aspect on Confucian theory of self-cultivation (Gongfu) were neglected. This paper explores ＂One principle runs through it all＂ and finds that the implications of its oneness aspect can be elaborated as ＂wholehearted concentration on every moment as it comes＂, ＂the unity of self and others＂, and ＂the consistency between root and branches＂, which means that it can be interpreted temporally and spatially, as well as according to Confucian teachings on simplicity. By the end, this paper concludes that filial piety and brotherly love are core mental cultivation method followed by King Yao, King Shun, Confucius and Mencius successively, which also implies ＂wholehearted concentration on every moment as it comes＂ and ＂the consistency between root and branches＂ and from which the unity between self and other people and that between self and other existence are derived. It also concludes that in Confucian teachings to gain knowledge as much as possible is aimed to run it all through one principle, and that principle is also the basis of gaining knowledge.