In plain words
Right at the very outset, a strange notion becomes apparent to us: that these are, in fact, the Ṛks — that is to say, they concern beings of radiant, luminous form. There are said to be many such gods, and Indra, Varuna, Mitra, and Parjanya are the names of some of them. These appear one after another. One such is Indra, the wielder of the thunderbolt, who has the reputation of bringing rain down to the earthly world. For this reason, Bharatiyas worship Indra.
'Indra' — that is, the mind that rules over the senses — came to be called Indra. He also has a second name, 'Puruhuta': 'puru' means many times or occasions, and 'huta' means one who is invoked. Indra, who is called the mind, is extolled in the Vedas as Rudra. When the mind is experiencing the world through the senses, that very mind is Indra. When, having conquered the senses, it attains the state of being the inner ruler present within all of them, that very mind is Rudra.
It is for this very reason that the Veda describes Indra and Rudra as two names for one and the same glorious deity. Any number of similar descriptions could be cited regarding the other deities as well; in the end, all of them come to be described in the same way.
They begin as gods. At last, as those with the entire universe dwelling within them, as witnesses present to every heart, as the lords over all the worlds,