Joseph Goldstein talks about Metta - Not Clinging. When the mind is not clinging, it's not agitated, and eventually, it attains Nirvana.
Liberation Through Not Clinging
A dharma talk where Buddhist teacher Joseph Goldstein discusses the nature of impermanence and letting go of the grasping mind.
All the Buddhist traditions converge in one understanding of what liberates the mind. It is summed up very succinctly in one teaching of the Buddha: "Nothing whatsoever is to be clung to as 'I' Or 'mine.' Whoever has heard this has heard all the teachings. Whoever practices this has practiced all the teachings. Whoever realizes this has realized all the teachings."
Nothing whatsoever is to be clung to as "I" or "mine." Not clinging can be understood on two levels. The first level is as a non-sectarian instruction for practice. What to do? Don't cling. There's no Buddhist school that says, "Cling." How to practice in the world? Don't cling. It hardly matters what form we build around that.
~From One Dharma by Joseph Goldstein