In this second chapter the discussion is between Maharshi Gargya and a King Jaatha satru.
In this chapter the detailed discussion of the brahma thathwam is given in which mind-intellect-vaak-indriyas-aathama thawa-paramaathwathathwa- god-divinity-awareness-consciousness etc are discussed in detail.
This chapter has six parts which are also known brahmanas.The third chapter has 9 brahmanas which discuss various aspects connected with the day to day spiritual life including that connected with yagaas. This chapter is narrated as the discussion between Maharshi Yajnavalkhya and Janaka Maharaja. In this chapter discussion includes the role of the priests of the yaagas, karma, karma phala, death, and the path of jeevathama after death, the role of sanyaasa, theknowledge of Vedas and its merits, the creation of various cosmic components including galaxies - planets-stars- comets-etc..
The secondpart of this chapter is the discussion between Maharshi Gargya andMaharshi Yajnavalkhya and the subject matter include 33 devathaas, 8vasus, 11 rudras and 12 aadithyas.
The last part of this chapter is the explanation given by Maharshi Sakalya. In the fourth chapter of the Upanishads discussion is focusing on various opinions/religions existed in ancient India which explain the brahma thathwam . These religions were known as Sailini matham, Udanka matham, Barku atham,Bharadwaaja matham, Saaklaya matham..
All these mathams are various descriptions given on the absolute truth which is the brahma thathwam. For a science student these descriptions can be combined as the awareness, consciousness and various forms of energy ( perhaps this subject is very deep and may not be in a position to understand for a common man). We all should understand that Bruhad aranyaka Upanishad is very tough to understand without a commentary.