大乘入道次第開決 1.116

1.116

由依定故方能離染等者。謂要依定方發輕安而離諸染。故說定是離染依也。

Regarding "it is only by relying on concentration that one can separate from defilement, etc.": this means that only by relying on concentration does one give rise to pliancy and separate from all defilements. Therefore, it is said that concentration is the support for separating from defilement.