(Source: Patanjali Yoga Sutra I. 33)

The essence:
Friendship, mercy, gladness, and indifference, being thought of in regard to subjects that are happy, unhappy, good, and evil respectively, shall pacify the Chitta.

We must have these four sorts of ideas. We must have friendship for all; be merciful towards those in misery; when people are happy, we ought to be happy; and to the wicked, we must be indifferent.

Same is the case with all subjects that comes before us. This aphorism of Patanjali indicates beautifully as to what kind of emotions or thoughts we will have to cultivate in our minds, in order to live peacefully with our surroundings.

Meaning:
With the cultivation of these sentiments of friendliness and loving kindness (maitri), mercy (karuna), joy and desire for the happiness of others (mudita), and equanimity (upeksanam) toward all beings and events, regardless if the events are auspicious or inauspicious (punya-apunya), or their conditional circumstances (visayanam), the underlying serenity and clarity of the citta (citta-prasadanam) is always cultivated and thus can manifest.

This powerful practice or cultivation (bhavanatas) as a attitudinal stance toward all beings and things in all circumstances will help maintain serenity and keep us centered in the heart (chitta-prasadanam). It will counteract polar imbalances of pleasure (sukha) or pain (dukha) caused by external events (visayanam), and prove to considerably enhance the continuous experience of the Eternal Reality — of All Our Relations.