Rashi on Genesis 38:30/רש"י על בראשית ל״ח:ל׳

1אשר על ידו השני THAT HAD THE SHINING RED THREAD UPON HIS HAND — The word יד is written here four times corresponding to the four acts of sacrilege which Achan, who was a descendant of Zarah, committed with his hand. Others say these correspond to the four things which he took with his hand of the spoil of Jericho: a Babylon garment, two hundred shekels, and a wedge of gold (Genesis Rabbah 85:14).

2ויקרא שמו זרח AND HIS NAME WAS CALLED ZARAH — (bright, shining), because of the bright colour of the scarlet thread.