"Ki Hi Chochmaschem U'Binaschem L'Eini HaAmim," (Devarim 4:6). This is the mitzva of calculating the calendar based on the moon. Rashi explains that if we do it correctly, the nations will consider us wise. If we make mistakes they will consider us fools. Why is it so critical how we appear in the eyes of the world?
Rav Shimshon Pincus answers that the nations are compared to the sun which
inherently gives off rays of light. Each nation has a dominant strength or ray
of light that characterizes its people. Bnei Yisrael, however, is compared to
the moon. The moon does not generate any of its own light and only reflects the
light of the sun.
Rav Shmishon tells a mashal about a home with many different things in it. It
has a table that has a specific function. Similarly, a bed, chair, spoon, and
fork all have specific functions. A mirror, however, has nothing. Yet, it can
look beautiful by reflecting the right things, or bare if it is dark and
reflects only the darkness.
Bnei Yisrael only shine when we reflect the light of Hashem. If we keep the
Torah, we will reflect a brilliant light and be respected by the nations.
However, if we choose the path of darkness, we will be totally void of any light
and be considered to be fools living in the dark by the nations of the world.