The theory of attaining Godhood and its proof has been mentioned in different Upanishads in various ways which are as follows:

BrihadAranyaka Upanishad(2.5.13) has mentioned-
“The shinning immortal Person who is in this mankind and with reference to oneself, this shinning immortal Person who exists as a human being- he is just this Soul, this Immortal, this Brahma, this All.”

Svetasvatara Upanishad(3..11) has mentioned-
Who is this face, the head, the neck of all; Who dwells in the heart of all beings; All pervading is He and bountiful; Therefore omnipotent and kindly(Siva).

KathaUpanishad (6.14) has mentioned-
When are liberated all; The desires that lodge in one’s heart; Then a mortal becomes immortal; Therein he reachesBrahma.

SvetasvataraUpanishad (4.3) has mentioned-
Thou art woman, Thou art man; Thou art the youth and the maiden too; Thou as an old man tottering with a staff; Being born, Thou becomest facing in every direction.

The era of Diamond reveals that a man may see all the sportive forms of God with all His attributes in dreams and becomes Brahma to be united with each human race bearing love for each other and be united in a point which is the first occurrence of its kind in the world history.