'Now that which is that subtile essence (the root of all), in it all that exists has its self. It is the True. It is the Self, and thou, O Svetaketu, art it.' 'Please, Sir, inform me still more,' said the son. 'Be it so, my child,' the father replied.

In plain words: The father says there is one fine, hidden essence that is the true self of everything that exists. It is the True, it is the Self, and 'you are that, Svetaketu.' Svetaketu asks to learn more, and his father agrees.