Maitri is friendship in Hinduism and is a quality that Sage Patanjali calls upon a seeker of peace to cultivate. In Yogasutra of Patanjali, various ways of making the mind peaceful and calm are described (1.33-39) for an aspirant who desires to make the mind stable.
By nature the human mind has an innate tendency to run after objects of enjoyment. As explained in Katha Upanishad (II.1.1), the creator of the universe has himself made the sense organs in such a way that they have a natural inclination to get attracted towards objects of enjoyment. They pull the mind outside and thus make it unsteady. That gives rise to an endless process of desire. Unless this process of desire is overcome completely, there is no possibility of making the unsteady and unstable mind peaceful.
Hence Sage Patanjali recommends that an aspirant on the path of Yoga must, first of all, bring about a basic change in the natural tendency of the mind to “run outside.”
This change can be brought about by several means. Cultivation of maitri and other attitudes is an important means recommended by Sage Patanjali (I.33).
If the aspirant learns to have an attitude of maitri (friendliness) towards all situations, that attitude helps to keep the mind unwavering. The other attitudes to be cultivated with maitri are karuna (compassion), mudita (joy) and upeksha (forgiveness).