। ॥ ६४८ ॥
In plain words
This ānanda you feel is a reflection, an image of bliss mirrored in the mind. So as merit gathers or thins, it rises and sinks — the reflection itself going high, then low.
Close to the Sanskrit
That this bliss is a reflection — which is mirrored in the mind — by the increase and the diminution of merit it becomes, itself, high and low.