Agatasatru said: 'Thus far only?' 'Thus far only,' he replied. Agatasatru said: 'This does not suffice to know it (the true Brahman).' Gargya replied: 'Then let me come to you, as a pupil.'

In plain words: Agatasatru asks Gargya if that is all he knows, and Gargya admits it is. The king says this is not enough to truly know Brahman. Gargya humbly asks to become the king's student.