The Moon is feminine and the Sun is masculine–cool silvery light and hot fire. So, when virility of the Sun or the hot glowing light unites with the cool light (matter) of the Moon, then whatever comes into being is formed and formless. Therefore, whatever you see here, says the Rishi, is itself matter.
Now, he says in the sixth sloka:
Athaaditya Udayanyat Praachiim Disham Pravishati
The Sun, after rising, enters the eastern side, by that he bathes in his rays all life that is in the East. When he illumes all the other sides–the North, the South, the West, above and below and in between, he bathes with his rays all living beings. This means, the Prana or life energy in the form of the sun’s light bathes the entire Universe in the four directions.
Sa Esa Vaisvaanaro Visvarupah
This is He, the Vaisvanaara fire, assuming every form. The verse of the Rig Veda declares that it is life and fire that rises everyday. Now, the Vaisvanaara is supposed to be the fire, which is the essence of living beings–the life, the Prana, the energy that glows in all human beings; while Visvarupah is the essence of the whole Universe. So, the Rishi says that this light that appears of the sun is the Vaisvanaara, the fire that assumes every form and rises everyday. This is what the Rig Veda says too. And, about the Vaisvanaara or the Supreme essence that pervades everything, the Upanishad declares: Visvarupam Harinam Jatavedasam.
Rishi says that this light that appears of the sun is the Vaisvanaara, the fire that assumes every form and rises everyday.