首楞嚴義疏注經 2.642

2.642

行以遷流造作為義，剎那無常，念念遷謝，生死死生如旋火輪，無有休息，故以瀑流，波浪相續，無踰越義以為喻也。

Formations has the meaning of flowing alteration and conditioned activity: moment by moment impermanent, each thought-instant passing away, birth and death, death and birth, like a whirled firebrand wheel with no rest; hence the rushing torrent, waves succeeding one another without crossing over, is used as a metaphor.