首楞嚴義疏注經 10.320

10.320

顯行相也。初二句標，行陰遷流，微細難覺，故云不住密移也。甲長下釋，前三句釋不住，後一句顯密移。

This reveals the characteristic of formations. The first two lines set forth the premise: the aggregate of formations shifts and flows, subtle and difficult to perceive; hence it says "does not halt, secretly shifting." From "nails grow" onward is the explanation: the first three lines explain "does not halt," and the last line reveals "secretly shifting."