Here is an essay on the Four Sublime States or Abodes. This essay explains the Buddha’s teaching on the importance of Loving Kindness (metta), Compassion, Sympathetic Joy and equanimity. All quotes will come from this essay.
accesstoinsight.org/lib/authors/nyanaponika/wheel006.html
Quotes in green will be directly from the teachings of the Buddha.
In Pali, the language of the Buddhist scriptures, these four are known under the name of Brahma-vihara. This term may be rendered by: excellent, lofty or sublime states of mind…
These four attitudes are said to be excellent or sublime because they are the right or ideal way of conduct towards living beings (sattesu samma patipatti). They provide, in fact, the answer to all situations arising from social contact. They are the great removers of tension, the great peace-makers in social conflict, and the great healers of wounds suffered in the struggle of existence. They level social barriers, build harmonious communities, awaken slumbering magnanimity long forgotten, revive joy and hope long abandoned, and promote human brotherhood against the forces of egotism.
They are called abodes (vihara) because they should become the mind’s constant dwelling-places where we feel “at home”; they should not remain merely places of rare and short visits, soon forgotten. In other words, our minds should become thoroughly saturated by them. They should become our inseparable companions, and we should be mindful of them in all our common activities. As the Metta Sutta, the Song of Loving-kindness, says:
When standing, walking, sitting, lying down,
Whenever he feels free of tiredness
Let him establish well this mindfulness —
This, it is said, is the Divine Abode.
These four — love, compassion, sympathetic joy and equanimity — are also known as the boundless states (appamañña), because, in their perfection and their true nature, they should not be narrowed by any limitation as to the range of beings towards whom they are extended. They should be non-exclusive and impartial, not bound by selective preferences or prejudices. A mind that has attained to that boundlessness of the Brahma-viharas will not harbor any national, racial, religious or class hatred…
Generally speaking, persistent meditative practice will have two crowning effects: first, it will make these four qualities sink deep into the heart so that they become spontaneous attitudes not easily overthrown; second, it will bring out and secure their boundless extension, the unfolding of their all-embracing range.
Here is the Metta Sutta, one of the most beautiful suttas in the Tipitaka.
*This is what should be done
By one who is skilled in goodness,
And who knows the path of peace:
Let them be able and upright,
Straightforward and gentle in speech,
Humble and not conceited,
Contented and easily satisfied,
Unburdened with duties and frugal in their ways.
Peaceful and calm and wise and skillful,
Not proud or demanding in nature.
Let them not do the slightest thing
That the wise would later reprove.
Wishing: In gladness and in safety,
May all beings be at ease.
Whatever living beings there may be;
Whether they are weak or strong, omitting none,
The great or the mighty, medium, short or small,
The seen and the unseen,
Those living near and far away,
Those born and to-be-born —
May all beings be at ease!
Let none deceive another,
Or despise any being in any state.
Let none through anger or ill-will
Wish harm upon another.
Even as a mother protects with her life
Her child, her only child,
So with a boundless heart
Should one cherish all living beings;
Radiating kindness over the entire world:
Spreading upwards to the skies,
And downwards to the depths;
Outwards and unbounded,
Freed from hatred and ill-will.
Whether standing or walking, seated or lying down
Free from drowsiness,
One should sustain this recollection.
This is said to be the sublime abiding.
By not holding to fixed views,
The pure-hearted one, having clarity of vision,
Being freed from all sense desires,
Is not born again into this world.*