大乘起信論義記 3.510

3.510

第三、結中言助成等者，如凡夫人，非不樂世間，無以勤修善行。約二乘人，非不怖生死，無以起於大悲。是故二行不相離也。言若止觀不具不能入菩提道者，止觀相須，如鳥兩翼、車之二輪，二輪不具則無運載之功，一翼若闕則無凌虛之勢，故云不具則不能入。

In the third part, the conclusion, stating "mutually assist and accomplish", etc.: as for ordinary persons, unless they do not take pleasure in the world, there is no way for them to diligently cultivate wholesome practices; in terms of the persons of the two vehicles, unless they do not fear birth and death, there is no way to give rise to great compassion. Therefore, the two practices are not separated from each other. As for stating that if calming and insight are not complete one cannot enter the path of bodhi: calming and insight depend on one another, like the two wings of a bird or the two wheels of a cart; if the two wheels are not complete, there is no capacity for carrying, and if one wing is lacking, there is no momentum for soaring into the sky; therefore, it is said that if they are not complete, one cannot enter.