सद्भावे साधुभावे च सदित्येतत्प्रयुज्यते।प्रशस्ते कर्मणि तथा सच्छब्दः पार्थ युज्यते॥
sad-bhāve sādhu-bhāve ca sad ity etat prayujyatepraśaste karmaṇi tathā sac-chabdaḥ pārtha yujyate
Word by word
The verse says
Sat is used for what is real and for what is good. And it is used, Arjuna, for an action worth doing.
In plain words
The third word does two jobs at once, and the two jobs turn out to be the same job.
Sat means what is real. Sat also means what is good.
That is not a pun. It is a claim. Goodness is not something added on top of reality. It is what reality looks like when nothing is being faked.
Where you've felt this · in friendship
A friend opens the door and you know in the first second whether he is actually pleased you came, or performing it. Nobody ever taught you how to do this. The real version does not have more signals in it than the performance. It has fewer, because nothing is being added.
Going deeper
One word meaning both real and good is the quiet claim at the end of this chapter, and it is not wordplay.
Sat is the participle of the verb to be: what is. It is also the ordinary word for good, true, worthy. One word, both jobs, for three thousand years.
The idea underneath is that falseness and badness are the same failure seen from two angles. A cruel act needs a false story about the person it is aimed at. A dishonest kindness needs a false account of why it is being done. Nothing bad is ever fully real, because something always has to go unlooked-at for it to proceed.
Which is a strange sort of encouragement. You are not being asked to add goodness to your life from outside, like a coat of paint. You are being asked to stop maintaining the places where you are not quite telling yourself the truth, and to see what is left.