सुखमात्यन्तिकं यत्तद्बुद्धिग्राह्यमतीन्द्रियम्। वेत्ति यत्र न चैवायं स्थितश्चलति तत्त्वतः ॥

sukham ātyantikaṁ yat tad buddhi-grāhyam atīndriyam vetti yatra na chaivāyaṁ sthitaśh chalati tattvataḥ

That in which he findeth the supreme delight which the Reason can grasp beyond the senses, wherein established he moveth not from the Reality;

In plain words: Krishna says in that state a person finds the greatest joy. This joy goes beyond the senses and is known by the understanding. Once there, he does not slip away from what is truly real.