Permanent Friendship - Verse 1

This verse, and the previous three in the Equanimity sequence are all variations of one intent – to end avidyā - what is opposed to vidyā - Self knowledge. Avidyā is, in Patanjali's words, the field for all other kleśa-perpetual causes of suffering.

The key words in this verse are Ātman – Self and anātman – not-Self.

The word ātman can refer to either jīvātman, the individual self identified with name and form, or Paramātman - the highest Self, transcending form. It is used in both senses in this Gītā verse in order to establish the right order between the two. In translation, the distinction between the two is made by capitalizing the latter.

The same words, ātman and anātman are used in the Yoga Sutras' definition of avidyā:
anityāśuci-duḥkhānātmasu
nitya-śuci-sukhātma-khyātir avidyā
The attributing of permanence, purity, happiness and self to impermanence, impurity, the painful, and nonSelf is avidyā.

Patanjali's formula states the primary conditions acting in opposition to one's Self, or the ways in which one acts just like an enemy. Avidyā is the not-Self opposition referred to in the verse.

The failsafe solution to this universal human trait of pursuing "happiness in what is really painful" is to practice the words of the previous verse (3): sama-duḥkha-sukhaḥ - remaining the same in pain and pleasure; the same in the increase or decline of income, praise or criticism, and what is pleasant or unpleasant.

Or elsewhere in the Gītā:
"not over-eager for pleasure nor discouraged by pain"

The word defined here as friend or enemy is the same word - ātman. We should consider the difference just a fine line of choosing to be the ātman who overrules the one putting up the opposition. And let's regard any of the many who support this, as a friend indeed.