Transliteration
nasti buddhir ayuktasya na cayuktasya bhavana
na cabhavayatah santir asantasya kutah sukham
Translation
One who is not in transcendental consciousness can have neither a controlled mind nor steady intelligence, without which there is no possibility of peace. And how can there be any happiness without peace?
Purport
The unsettled mind can’t have peace and happiness
In earlier shlokas (#60-65) Bhagvan Shri Krishna explained Arjuna about the glory of Buddhi, the yoga to establish intelligence into Ishwar(Bhagvan Shri Krishna). One who is able to establish his intelligence in Bhagvan gets control over his mind and senses. One who has the mind and senses controlled to get peace and happiness.
In this Shloka, Bhagvan Shri Krishna, explains that for those whose intelligence is not established into the devotion of Ishwara, he may find his mind dwelling in the physical world. One whose mind is not stable cannot have peace. And without peace one cannot get happiness even though he has all worldly wealth.
