The Nyāya Sūtras is an ancient Indian Sanskrit text composed by Akṣapāda Gautama, also known as Aksapāda, and is the foundational text of the pracina or Old Nyaya school of Hindu philosophy.
The text contains 5 parts divided further into chapter and contains over 500 sutras.
Babaji is reading from Nyāya-darśanam with the Vātsyāyana's bhāsya, which includes the Hindi commentary by Dhundhiraj Shastri.
The spiritual world is not somewhere else. It is right here. It depends on your angle of vision – same place, same thing is now different. Like a tv with 100 channels, it depends on which channel. Whatever show you are watching, you are absorbed in that show. All is there, all the channels are hanging in the same ether – depending on where you tune to, you see that. Krishna is right here, but you are not tuned to Him.