Why is the sun the greatest light source?

The star around which the Earth revolves, and the planet's source of light and heat, hence life. The Sun is the star at the center of the Solar System. The Earth and other matter (including other planets, asteroids, meteoroids, comets and dust) orbit the Sun, which by itself accounts for more than 99% of the solar system's mass. Energy from the Sun—in the form of insolation from sunlight—supports almost all life on Earth via photosynthesis, and drives the Earth's climate and weather.

https://www.universetoday.com/16338/the-sun/

The Sun, our Sun is the ONLY source of light, Energy, Life and Heat that The Earth uses.

ALL life has come from Stars, of which the Sun is one.

The sun is not our only source of light, thousands of stars light up our night skys. Yet these stars, which are they themselves very distant suns, are mere twinkles compared to the sun's brillance.

There are Billions and Billions (say it like Sagan) of Stars but none of the supply a usable source of light for us here on Earth!

Strictly, as the question is worded, the Sun isn't the greatest source of light. It is insofar as we down here are concerned, but there are more powerful sources of light way off. Why don't we get more light from the billions and billions of stars? This is the problem that's known as Olber's paradox (although it goes back as far as Kepler in origin). See http://math.ucr.edu/home/baez/physics/Relativity/GR/olbers.html for an explanation better than I can give.