What does Genesis 38:29 mean?

Tamar's twins are being born (Genesis 38:18, 24–26). As Genesis has made abundantly clear in the telling of Esau's and Jacob's story, birth order mattered a great deal in the ancient world. The oldest son will, by custom, hold both the birthright and the family blessing. Part of God's unique interaction with Israel was a constant disruption of this tradition (Genesis 25:23). In this case, one of the twins thrust out a hand before the other could emerge. Those familiar with childbirth would see this as a sign of an unusual, likely difficult labor.

A clever midwife tied a red thread around the wrist, indicating a firstborn son. Unexpectedly, however, the hand was drawn back, and the other baby was delivered first. In response, the midwife addresses the baby's remarkable breach. This leads to the boy—technically considered the younger twin—being named Perez, which means "break through."