The Perfection of Loving-kindness - The four divine abidings

Loving-kindness, metta, is one of the divine abidings, brahmaviharas. There are four of them: loving-kindness, metta, compassion, karuna, sympathetic joy, mudita and equanimity, upekkha. Metta is adosa cetasika, the reality of non-hate or non- aversion. Compassion is karuna cetasika, which arises when one supports someone else, wanting to alleviate his suffering and trouble. Sympathetic joy is mudita cetasika, which arises when one rejoices in someone else’s happiness. Equanimity, upekkha, is tatramajjhattata cetasika, evenmindedness which is the absence of attachment and aversion. It arises when one understands the true nature of anatta, non-self. 
When metta, adosa cetasika, arises we are at that moment free from hate or aversion. When karuna cetasika arises, we are concerned about someone who suffers and want to assist him. When someone else is happy because of gain, honour or praise, and we also rejoice in his happiness, there is mudita cetasika. When we have no lobha or dosa and we are evenminded and impartial towards all beings, there is tatramajjhattata cetasika, which is the brahmavihara of upekkha, equanimity.
If someone wants to extend metta towards a person who conducts himself in an unpleasant and irritating way, he should, to begin with, develop adosa cetasika, the reality that is freedom from anger.
The brahmaviharas, divine abidings, of loving-kindness, compassion, sympathetic joy and equanimity are dhammas which are faultless and superior. A person with metta is faultless and when he extends metta to someone else he is superior. The practice of the four brahmaviharas is the right practice towards all beings. We read in the “Atthasaliní” (I, Part V, XIII, The Divine States, 195):

“And as Brahma divinities live with faultless thoughts,

so aspirants associated with these four states live like the Brahmas.

Thus, because of the meaning of ‘divine’ and of their faultless nature,

they are called ‘Divine States’.”
These four divine abidings lead to calm, to non-disturbance and they are faultless. They are the way leading to purity. There is a particular order in the cultivation of the four brahmaviharas, metta being the first, since each of them is a supporting condition for the following brahmavihara. We read in the “Atthasalini” (same section, 196) why they are without limits:

“And all of them arise in an immeasurable field,

therefore are they called the ‘Immeasurables’.

For beings without limit constitute their field (object).”