Text 6

 bandhur atmatmanas tasya
yenatmaivatmana jitah
anatmanas tu satrutve
vartetatmaiva satru-vat

 Translation

For him who has conquered the mind, the mind is the best of friends; but for one who has failed to do so, his mind will remain the greatest enemy.

Commentary by Srila Prabhupada 

The purpose of practicing eightfold yoga is to control the mind in order to make it a friend in discharging the human mission. Unless the mind is controlled, the practice of yoga (for show) is simply a waste of time. One who cannot control his mind lives always with the greatest enemy, and thus his life and its mission are spoiled. The constitutional position of the living entity is to carry out the order of the superior. As long as one’s mind remains an unconquered enemy, one has to serve the dictations of lust, anger, avarice, illusion, etc. But when the mind is conquered, one voluntarily agrees to abide by the dictation of the Personality of Godhead, who is situated within the heart of everyone as Paramatma. Real yoga practice entails meeting the Paramatma within the heart and then following His dictation. For one who takes to Krishna consciousness directly, perfect surrender to the dictation of the Lord follows automatically.

Commentary by Sri Visvanatha Cakravarti Thakur

The mind is whose friend and whose enemy? This verse answers. The mind (atma) is a friend, causing benefit, to that jiva who has conquered the mind. The mind acts as an enemy, causing harm, to that jiva who does not control the mind (anatmanah).