(Extract from SN 46.54 Mettam Sutta - http://www.accesstoinsight.org/tipitaka ... .wlsh.html ...)
"And how, monks, does a monk cultivate the heart's release by loving-kindness? What is its goal, its excellence, its fruit and its outcome?
"In this case, monks, a monk cultivates the enlightenment-factor of mindfulness accompanied by loving-kindness and similarly the enlightenment-factors of investigation-of-states, energy, rapture, tranquillity, concentration, equanimity, accompanied by loving-kindness which is based on detachment, dispassion, leading to maturity of surrender. If he wishes to dwell perceiving the repulsive in what is not repulsive, he dwells thus perceiving the repulsive. If he wishes to dwell perceiving the unrepulsive in what is repulsive, he dwells thus perceiving the unrepulsive. If he wishes to dwell perceiving the repulsive both in what is repulsive and what is not repulsive, if he wishes to dwell perceiving the unrepulsive in both..., he dwells thus. If he wishes, avoiding both the repulsive and unrepulsive, to dwell equanimous, mindful and clearly aware, he dwells thus, equanimous, mindful and clearly aware, or, attaining the heart's release called 'beautiful' he abides there. I declare that the heart's release by loving-kindness has the beautiful for its excellence. This is the attainment of a wise monk who penetrates to no higher release.
1.The four Brahma-vihaaras ("divine abidings"), also called the four "boundless (appamañña) states," are: 1. Loving-kindness (mettaa), 2. Compassion (karu.naa), 3. Sympathetic Joy (muditaa), 4. Equanimity (upekkhaa).
2.Upekha, the adjective from upekkhaa. "Equanimous" is a rare word in modern English, but is less misleading than "indifferent." It is used by the Ven. Ñanamoli in The Path of Purification (Visuddhimagga) (Colombo 1956).
3.Sato sampajaano. The old rendering (introduced by T. W. Rhys Davids) "mindful and self-possessed" dies hard, but is far too vague, if not positively misleading. The real meaning of sampajaana is "clearly aware": see BD [Buddhist Dictionary (2nd ed.), by Ven. Nyaa.natiloka, Ven. Nyaa.naponika (ed.) (Colombo 1972)] s v. sampajañña.
4.Subha. This is explained in MN 77 as being associated with the fourth (lower) jhaana (SN 40.9, n. 2).
5.Cf. VM IX, 76: "If unable to reach higher than the attainment of loving-kindness and attain Arahantship, then when he falls from this life, he reappears in the Brahma world as one who wakes up from sleep."