EXTRA · Parashas Vayeishev · Passuk 38:30 · not a Torah Temimah citation on this passuk
Afterward his brother came out, on whose hand was the crimson thread; he was named Zerah.hZerah I.e., “brightness,” perhaps alluding to the crimson thread.
Classical source (EXTRA side-ring): Bereshis Rabbah 85:14.
Sefaria — Bereshis Rabbah 85:14
English: “And he called his name Zerach” — after the shining forth, for his hand shone forth first.
Derash on the verse (Bereshis Rabbah) — not a formal named middah of the 13. Name follows the visible first sign at birth.
Zerach’s name records that his hand appeared first, while Peretz took the birthright of emergence.