When we Jews study Torah and do our mitzvahs we are showing the world who HaShem is and thus we express the true nature of G-d and we become the light unto the world.
“Moses then taught the Jewish people the laws of legal testimony and perjury
[Moses told the Jewish people, “In any court case,] the matter [of a defendant’s innocence or guilt] must be confirmed by the testimony of [at least] two witnesses.” Deuteronomy 19:15
It is the Torah’s position that creation itself testifies to the existence of the Creator, as well as to the fact that His power lies beyond our ability to comprehend. However, the notion that G‑d’s essence is not only beyond our ability to understand but beyond our ability to conceive does not follow from examining the world; this truth must be established by “external” witnesses.
The witnesses to the inconceivable nature of G‑d’s essence are the Jewish people. By studying the Torah and performing G‑d’s commandments, the Jewish people introduce the world to the ineffability of G‑d’s essence, paradoxically accomplishing the categorically impossible feat of expressing what is by nature inexpressible.1 Likutei Sichot, vol. 19, pp. 188–196