Hashgachah Pratis in the Sefarim Hakedoshim

We Know That Hashem Will Make a Miracle for Us

What nation is there in all the world like Am Yisrael, who know the customs and laws of their G-d? It is customary in the world that a person who knows that he is to be judged wears black clothing and allows his hair and nails to grow, since he does not know what his verdict will be – whether he will emerge innocent or guilty. But Bnei Yisrael don’t do this. Rather, on Rosh Hashanah, the Day of Judgment, they wear white clothing and cut their hair and their nails, and eat and drink in joy, since they know that Hashem will make miracles for them.

Talmud Yerushalmi, Rosh Hashanah 1:3, cited in the Tur siman 581