華嚴經探玄記 11.36

11.36

第九堪受中，論名堅固力，謂是精進於上八行遍能策進，故云如是功德，即信等也。然精懃有二：一自分成處無退捨、二勝進分中修不息，堅心辨此名堪受力。

Ninth, in being capable of endurance, the Treatise calls it the power of firmness, meaning it is vigor universally able to urge forward the above eight practices; hence it says "such merits", which refers to faith and so on. However, diligent vigor has two aspects: (1) in the portion of one's own level, having achieved it, there is no regress or abandonment; (2) in the portion of superior progress, cultivating without cessation; discerning this with a firm mind is called the power of endurance.