Judah had a very complicated family life...
Bible Reading: Genesis 38
27: And it came to pass in the time of her travail, that, behold, twins were in her womb. 28: And it came to pass, when she travailed, that the one put out his hand: and the midwife took and bound upon his hand a scarlet thread, saying, This came out first, 29: And it came to pass, as he drew back his hand, that, behold, his brother came out: and she said, How hast thou broken forth? this breach be upon thee: therefore his name was called Pharez. 30: And afterward came out his brother, that had the scarlet thread upon his hand: and his name was called Zarah.
John's Midrash
A. Judah was the 4th of Jacob’s sons out of his first wife Leah. Judah had 3 sons with his wife Shuah, and 2 with his son’s widow, Tamar. Judah was also Joseph’s half-brother.
B. Shuah was Judah’s wife. Technically, her father was named Shuah, she is known in the Bible only as “the daughter of Shuah”. Furthermore, perhaps I am trying to make an honest woman out of her by suggesting that she and Judah were married. The Biblical text says simply, “and [Judah] took her, and went in unto her...”
C. Tamar was picked by Judah to marry his eldest son Er. When God killed Er, Judah made his second son Onan marry and “go in unto Tamar”. Onan ejaculated on the ground so God killed him. Judah had promised her his 3rd son Shelah as husband when he grew up. When this didn’t happen, Tamar dressed up like a harlot and seduced Judah, her own father-in-law.
D. Er was Judah’s firstborn son. Unfortunately for Er, He was found to be quite “wicked in the sight of the LORD”, and naturally, God slew him. The exact nature of his wickedness is unspecified. Perhaps as the artist’s rendering sugeests, it was Er’s extreme homeliness that offended God to the point of homicidal rage.
E. Onan was Judah’s 2nd son. After God slew Er, Judah demanded that Onan marry his brother’s widow Tamar. When it was time for Onan to "“go in unto” Tamar, he ended up pulling out and ejaculating on the ground because he refused to “give seed to his brother.” This “thing which he did displeased the LORD”, so naturally, He slew Onan also. The word “onanism”, which refers to masturbation, derives from this popular Bible story.
F. Shelah was the 3rd of Judah’s sons and next in line to take over husbandly duties with Tamar. Tamar waited for Shelah to grow up but once that finally occurred, for some reason, Tamar “was not given unto him to wife.” She then replaced her mourning clothes with a harlot’s veil, and seduced her father-in-law Judah and became pregnant by him with twin sons. Craftily, she demanded some tokens from him in exchnage for sex, which later proved to Judah that he was indeed the boys’ father.
G. Pharez was the firstborn of the twin sons Tamar had as a result of her union with her father-in-law Judah.
H. Zarah was the 2nd born of the twin sons Tamar had as a result of her union with Judah. Zarah tried to get credit as firstborn by sticking his hand out of the birth canal. It almost worked: “the midwife took and bound upon his hand a scarlet thread saying, This came out first.” Zarah then retracted his hand and brother Pharez popped out first.