Krishna begins His answer by describing the gunatita's relationship with the gunas themselves. When illumination (sattva's hallmark), activity (rajas's hallmark), or delusion (tamas's hallmark) arises, the gunatita does not resent them. And when they subside, they do not crave their return.
Imagine sitting on a riverbank, watching the water. Sometimes the current is clear and calm. Sometimes it rushes fast and muddy. Sometimes it barely moves at all. The person on the bank sees all of this but does not jump in to push the water one way or another. They observe without being swept away.
This is a radical inner freedom. Most people love their sattvic moods and fight their tamasic ones. The gunatita has stepped back from that struggle entirely. They witness the play of the gunas in their own body and mind without identifying with any of it.