Genesis 38:1
38:1 And it came to pass at that time, that {a} Judah went down
     from his brethren, and turned in to a certain Adullamite,
     whose name [was] Hirah.

     (a) Moses describes the genealogy of Judah, because the
         Messiah should come from him.

Genesis 38:2
38:2 And Judah saw there a daughter of a certain Canaanite,
     whose name [was] Shuah; {b} and he took her, and went in
     unto her.

     (b) A relationship which nonetheless was condemned by God.

Genesis 38:8
38:8 And Judah said unto Onan, Go in unto thy brother's wife,
     and marry her, and raise {c} up seed to thy brother.

     (c) This order was for the preservation of the stock, since
         the child begotten by the second brother would have the
         name and inheritance of the first: a practice which is
         abolished in the New Testament.

Genesis 38:11
38:11 Then said Judah to Tamar his daughter in law, {d} Remain a
      widow at thy father's house, till Shelah my son be grown:
      for he said, Lest peradventure he die also, as his
      brethren [did]. And Tamar went and dwelt in her father's
      house.

      (d) For she could not marry in any other family so long as
          Judah would retain her in his.

Genesis 38:16
38:16 And he turned unto her by the way, and said, Go to, I pray
      thee, let me come in unto thee; (for he {e} knew not that
      she [was] his daughter in law.) And she said, What wilt
      thou give me, that thou mayest come in unto me?

      (e) God miraculously blinded him so that he could not know
          her by her voice.

Genesis 38:20
38:20 And Judah sent the kid by the hand of his {f} friend the
      Adullamite, to receive [his] pledge from the woman's hand:
      but he found her not.

      (f) That his wickedness might not be known to others.

Genesis 38:23
38:23 And Judah said, Let her take [it] to her, lest we be {g}
      shamed: behold, I sent this kid, and thou hast not found
      her.

      (g) He fears man more than God.

Genesis 38:24
38:24 And it came to pass about three months after, that it was
      told Judah, saying, Tamar thy daughter in law hath played
      the harlot; and also, behold, she [is] with child by
      whoredom. And Judah said, Bring her forth, and let her be
      {h} burnt.

      (h) We see that the Law, which was written in man's heart,
          taught them that adultery should be punished with
          death, even though no law had been given yet.

Genesis 38:26
38:26 And Judah acknowledged [them], and said, She hath been {i}
      more righteous than I; because that I gave her not to
      Shelah my son. And he knew her again {k} no more.

      (i) That is, she ought rather to accuse me than I her.
      (k) for the horror of the sin condemned him.

Genesis 38:29
38:29 And it came to pass, as he {l} drew back his hand, that,
      behold, his brother came out: and she said, How {m} hast
      thou broken forth? [this] breach [be] upon thee: therefore
      his name was called Pharez.

      (l) Their heinous sin was signified by this monstrous
          birth.
      (m) Or the separation between you and your brother.