। ॥ ५०९ ॥
In plain words
What keeps this whole round of saṃsāra turning is adhyāsa — superimposition, one thing laid over another until the object is taken exactly backwards. And the root of adhyāsa, they say, is avidyā, ignorance, whose one defining act is to cover over.
Close to the Sanskrit
Of this transmigration the cause is superimposition, which is the inversion of the object; the root of superimposition they declare to be ignorance, whose characteristic is veiling.