On one occasion the Blessed One was dwelling at Sāvatthī in Jeta’s Grove, Anāthapiṇḍika’s Park. There the Blessed One addressed the bhikkhus: “Bhikkhus!”
“Venerable sir!” those bhikkhus replied. The Blessed One said this:
“Bhikkhus, when the liberation of the mind by loving-kindness has been pursued, developed, and cultivated, made a vehicle and basis, carried out, consolidated, and properly undertaken, eight benefits are to be expected. What eight?
(1) “One sleeps well;
(2) one awakens happily;
(3) one does not have bad dreams;
(4) one is pleasing to human beings;
(5) one is pleasing to spirits;
(6) deities protect one;
(7) fire, poison, and weapons do not injure one; and
(8) if one does not penetrate further, one moves on to the brahmā world.
“When, bhikkhus, the liberation of the mind by loving-kindness has been pursued, developed, and cultivated, made a vehicle and basis, carried out, consolidated, and properly undertaken, these eight benefits are to be expected.”
For one who, ever mindful, develops
the fetters thin out as he sees
the destruction of the acquisitions.
If, with a mind free from hate,
one arouses love toward just one being,
one thereby becomes good.
Compassionate in mind toward all beings,
the noble one generates abundant merit.
Those royal sages who conquered the earth
with its multitudes of beings
traveled around performing sacrifices:
the horse sacrifice, the person sacrifice,
sammāpāsa, vājapeyya, niraggaḷa.
All these are not worth a sixteenth part
of a well-developed loving mind,
just as the hosts of stars cannot match
a sixteenth part of the moon’s radiance.
One who does not kill or enjoin killing,
who does not conquer or enjoin conquest,
one who has loving-kindness toward all beings
harbors no enmity toward anyone.
Source: https://suttacentral.net/an8.1 Mettā Sutta AN 8.1 AN iv 150