The child of yibum with brother's widow is his reincarnation (Vayeshev)

Tamar succeeded in making Judah sleep with her. This way, Judah performed a "yibum," also known as "marrying brother's widow." Previously, Judah's son Onan did a "yibum" with Tamar, his brother's Er widow. Judah's act with Tamar could qualify, by stretch, as a "yibum."

The secret of yibum is that the child born of such a union is a reincarnation of the brother who passed away. This worked. Tamar had twins, and they were reincarnations of her two previous husbands. In their new lives, they corrected their previous mistakes.

The midwife marked the firstborn by tying a red thread on his hand - because their previous mistake involved hands. Zerah, who is the reincarnation of Onan, gave his hand first. He felt that he was not as bad as Er because he at least had a reason, not wanting to have a child in this brother's name. Still, he got a thread whose color was red - because he was not wholly blameless.

Art: Judah and Tamar by Arent de Gelder