Bhagavad Gita, Chapter 2 verse 55: Krishna responds: Having left behind all desires and being content in the Self through the Self alone, one has gained steady intellect.
When we serve the desires of others, we innocently renounce our own. So to speak, we leave 'behind all desires' to find happiness and contentment in objects of the senses. Desires, through the offices of the senses, no longer grip the mind and drag it out into the ever-changing, unstable and unpredictable material world (2.49). Intellect, the mind's faculty to determine what is real and true, steadies. Through the ego, the subtlest quality of intellect, we realize who we really and truly are, unbounded inner contentment, the Self (2.45). Through 'steady intellect' we become 'content in the Self through the Self alone.' That is, for the 'steady intellect' contentment is single-sourced to the Self alone.
copyright Keith R Parker 2021