The body of the individual self depends on food and drink for its birth and growth. Similarly, his thinking (sankalpa), physical contact (sparsha), and looking (drishti) at things produce his attachment (moha). This attachment determines his behavior, and his behavior ultimately results in his assumption of various forms. (Shvetashvatara Upanishad 5, 11)
There is nothing higher than or different from Him. Nothing is greater or minuter than Him. Seated in His own glory He stands like a tree, one without a second and immovable. By that Purusha (Supreme Being) the whole universe is filled (pervaded). (Shvetashvatara Upanishad 3, 9)
In this vast wheel of Brahman, which creates all things and in which all things rest, the living being flutters about, thinking – my silent self and the world are two different things. But in truth they are not different. Some wise people see them as one, and those people rest in evenness. They gain eternal happiness.
Just as a mirror shines bright once it has been cleaned of dust, so those who have seen the Self shine in mind and body. They are always and forever filled with happiness.
Only by knowing the Self does on become immortal. There is no other path.