Buddhi is the precious capacity to discriminate between what is pleasant for the moment and what is fulfilling always. In the chariot image from the Katha Upanishad a few verses earlier, buddhi is the charioteer.
Easwaran defines buddhi as the faculty of discriminative intelligence that, when guided by the Atman, steers the self away from transient pleasure toward lasting fulfilment.
, The Bhagavad Gita for Daily Living: A Verse-by-Verse Commentary, 1975thesis