東晉孫登首用「重玄」觀念注解《老子》，從南北朝到隋唐，道教人士以「重玄」解説《老子》、《莊子》或藉以闡發道教義理者甚眾，後人稱之為「重玄學派」。成玄英為初唐重玄學派重要的代表性人物，《道德經義疏》一書則為成玄英思想的奠基之作，其內容是以「重玄」的理路，建立虛通之理的本體之境，以及注重智悟的心性修為工夫。此書之學術地位有三：一就老子學而言，有綰合學術與宗教，總結前人諸説之色彩。二就中國思想史之發展而言，似可以視為繼魏晉玄學之後，道家思想發展的第三期，是玄學與佛教般若學的融合。三就影響而言，是道教史上最富哲學意味的學派，其思想影響了宋元內丹心性之學；而「重玄」的道理、心性諸説也可能啟發了宋明理學的發展。

Sun Deng of the Eastern Jin Dynasty is the first man who annotated Laozi with concept of Twofold Mystery. From the Southern and Northern Dynasties to the Sui and Tang Dynasties, lots of Taoists commentated Laozi and Zhuangzi or elucidated Taoism with Twofold Mystery. Posterity called them School of Twofold Mystery. Cheng Xuan-ying is important representative of School of Twofold Mystery in Early Tang Dynasty. Dao De Jing Yi Shu is the foundational work of Cheng Xuan-ying’s thoughts. The content is to discuss Metaphysics with Twofold Mystery and narrate the process of cultivation and realization of pure mind based on mind and nature. This book’s academic status can be generalized into three aspects： Firstly, as far as Laoism is concerned, it has color of linking academic and
religion and concluding all theories of predecessors. Secondly, as far as development of History of Chinese Thoughts is concerned, it seems to be seen as the third period of Taoism thoughts’ development after Xuanxue of the Wei and Jin Dynasties. It is a fusion of Xuanxue(literally “mysterious learning”, also known as Neo-Taoism) and Buddhism Prajñā (Wisdom in Buddhism). Thirdly, as far as influence is concerned, it is the best school that is rich in philosophy significance in Taoism history. The thoughts influenced Science of Mind-Nature and Inner Alchemy (Neidan) of the Song and Yuan Dynasties. Moreover, Twofold Mystery
and Theory of Mind-Nature were likely to enlighten the development of Neo-Confucianism.