Genesis 38 takes a seemingly unwarranted departure from the story of Joseph to give us an all-too-intimate account of Judah’s personal affairs. Why is Judah’s personal life important enough to spill right in the middle of an unrelated larger narrative?

While the interlude seems out of place, the prominence of Judah and his family lineage in the later history of Israel shows that this account was in fact warranted. It would indeed be Judah and Joseph (specifically, Ephraim) who would always be vying for imminence.

And rightly so. There would not be one single tribe given chief honors, because the one to whom it rightly belonged, Rueben, was counted unworthy.

1 Chronicles 5:1 Now the sons of Reuben the firstborn of Israel, (for he was the firstborn; but, forasmuch as he defiled his father’s bed, his birthright was given unto the sons of Joseph the son of Israel: and the genealogy is not to be reckoned after the birthright.
2 For Judah prevailed above his brethren, and of him came the chief ruler; but the birthright was Joseph’s:)

The chief ruler would come of Judah, but the birthright (of a double portion of the inheritance), normally accorded to the firstborn, would instead go to Joseph—specifically, his two sons, who each received an equal portion with their uncles, the other 11 tribes.

So, seeing as Judah would supply the chief ruler, rather than Rueben, the eldest, ruling his brethren, it became necessary to document the strange tangle through which that right would be passed down. All the more so because it would ultimately have to fall to none other but our Lord himself.

And so with that in mind, let us consider Genesis 38.

Genesis 38:1 And it came to pass at that time, that Judah went down from his brethren, and turned in to a certain Adullamite, whose name was Hirah.
2 And Judah saw there a daughter of a certain Canaanite, whose name was Shuah; and he took her, and went in unto her.
3 And she conceived, and bare a son; and he called his name Er.
4 And she conceived again, and bare a son; and she called his name Onan.
5 And she yet again conceived, and bare a son; and called his name Shelah: and he was at Chezib, when she bare him.

Judah fathers three sons, but Er is the eldest, so he will have the birthright and will be the chief among his brethren.

6 And Judah took a wife for Er his firstborn, whose name was Tamar.
7 And Er, Judah’s firstborn, was wicked in the sight of the LORD; and the LORD slew him.

However, like Reuben, he is rejected. Before he can produce seed, he is destroyed.

8 And Judah said unto Onan, Go in unto thy brother’s wife, and marry her, and raise up seed to thy brother.

Thus, as was customary, his younger brother would have to supply Er an heir. Though Onan would be his father, the son would be counted after Er’s lineage, and thus would be chief and receive the birthright of Er.

9 And Onan knew that the seed should not be his; and it came to pass, when he went in unto his brother’s wife, that he spilled it on the ground, lest that he should give seed to his brother.
10 And the thing which he did displeased the LORD: wherefore he slew him also.

But neither is Onan counted worthy, and so he also perishes. We can see how closely God was watching over the lineage that would rule Israel and produce the promised Messiah.

It seems that Judah doubted if Shelah, his third son, would be accepted either, and so he deferred to give Tamar to be his wife. Eventually Tamar became impatient, and tricked Judah into fathering a child through her. Or rather, two children.

Genesis 38:27 And it came to pass in the time of her travail, that, behold, twins were in her womb.

What this means, is that God honored Tamar, taking away her reproach, by giving her a son to take the name of each of her prior husbands. That is, she would still bear the heirs of both Er and Onan, and thus she would also still bear the chief who would have the birthright of Judah. And by a strange twist of fate, the children who would have been traditionally counted among Judah’s direct heirs, would actually be his own sons, and not his grandsons.

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.

We can see why it was so important to identify which one was the eldest—he would not just be Tamar’s eldest, but actually assume the place of Judah’s eldest son, though the forth born.

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.

So Pharez became the chief and whose was the birthright of Judah, his firstborn. And thus it would be through him that the chief ruler would arise, and through whom would descend the Messiah. He displaced 5 others to gain this position:

1. Reuben
2. Er
   
3. Onan
   
4. Shelah
   
5. Zarah

Five is the number of divine appointment in scripture, and it is most clear that God had a plan prepared which these 5 were not found worthy to fulfill. But with Pharez, the sixth, he found his man.