Nibbana is an object – we don’t know this kind of object, but we can know our mind.
When the mind has lobha, we can know; when the mind has defilement, we can know. Also, when the mind has no defilement, we can know – we can understand, we can experience with the mind.
When the mind is purified, when it has no more defilement, then it chooses its object. Mind and object must match.
Only a purified mind can catch the nibbana object.