釋禪波羅蜜次第法門 8.42

8.42

遍行者，觀行未利，亦並約心而觀四諦，名為大行。今觀道稍利，能遍歷諸緣，觀於四諦，出十六行觀，故名遍行。

As for 'pervasive activity': when the observational practice is not yet sharp, one also observes the four truths based together on the mind, which is called great activity. Now when the path of observation becomes somewhat sharper, one is able to traverse all conditions pervasively, observing the four truths and producing the observation of the sixteen modes of practice; hence it is called pervasive activity.