He who knows thus, attains after desisting from this world, this self made of food. After attaining this self made of food, then attaining this self made of mind, then attaining this self made of vital force, then attaining this self made of mind, then attaining this self made of intelligence, then attaining this self made of bliss, and roaming over these world with command over food at will and command over all forms at will, he continues singing this sama song: "Halloo! Halloo!Halloo! I am the food, I am the food; I am the eater; I am the unifier, I am the unifier, I am the unifier; I am (Hiranyagarbha) the first born of this world consisting of the formed and the formless, I as Virat) am earlier than the gods. I am the navel of immortality. He who offers me thus (as food), protects me just as I am. I, food as I am, eat him up who eats food without offering. I defeat (i.e. engulf) the entire universe. Our effulgence is like that of the sun. This is the Upanisad.
This indeed is the great 'Halloo' and world encompassing bliss. In Bangalore I met an Australian devotee of a teacher whose method of instruction was the progressive move through the koshas manomaya kosha, pranamaya kosha etc. as in the Upanisad.
I was brought to the teacher's house and there it was explained to me how he had come to this teaching. He had fallen ill of a fever and it seemed to him had left his body. (Stop me if you've heard this before.) In that sphere in which he now was he met the Septa Rishi (Seven Sages) who looked surprised to see him. What are you doing here, you're not supposed to be here for many years. We are going to send you back but with a teaching method that when it is transmitted to a suitable person and practiced faithfully for 15 minutes a day will definitely bring on a state of samadhi within a few years.
As an analogy for the progression through the koshas he offered the image of a series of airlocks in a space-ship. His own meditation space was behind a recess in a wall with a grill in front of it about 3'x3'. We talked outside it and there was a definite vibration of peace at that spot. That's totally subjective of course, just me projecting my own great 'halloo'.