"Judah named him Peretz…. Judah named him Zerach" (Gen. 38:28-30):

In the Kabbalistic work Sefer HaBahir, Zerach (in Hebrew, "shining") is associated with the sun which shines constantly, and Peretz (in Hebrew, "breaking through") is associated with the moon which experiences periods of "brokenness" and rebirth.1

Metaphorically, the sun represents the completely righteous whose light shines consistently, without interruption or fluctuation. The moon represents the penitents who have done wrong but change their ways and return to G‑d. Much like the moon, penitents are in a perpetual process of rise and fall, diminished light and increased light.

Penitents achieve what the consistently righteous cannot.

Yet because of their challenges, the penitents reach a higher spiritual level and achieve what the consistently righteous cannot.2 Thus, Peretz, who is associated with the moon and is therefore the archetype of repentance, precedes Zerach and is the firstborn, since the accomplishments of the penitents surpass those of the consistently righteous.

The fact that Zerach stretched his hand out first represents the notion that we must aspire to be completely righteous. But because Achan would eventually emerge from him, Zerach needed the revelation of the phenomenon of repentance to precede his own birth, thereby providing Achan the means with which to rectify his misdeed. (See Joshua 7)

Adapted from Likutei Sichot, vol. 30, pp. 188-189
© 2001 Chabad of California/www.LAchumash.org