At that time (After all waves have finished. This is nothing to take with concentration)the seer (Purusha) rests in his own (unmodified) state.
In plain words: When the thought-waves stop, the seer, our true Self (Purusha), rests in its own natural state. It is like a lake going still so you can see the bottom.
As soon as the waves have stopped, and the lake has become quiet, we see its bottom. So with the mind; when it is calm, we see what our own nature is; we do not mix ourselves but remain our own selves.
Namaste.
A calm guide to life, the mind and the old teachings.