Genesis 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 knew not that she was his daughter in law.) And she said, What wilt thou give me, that thou mayest come in unto me? And he turned unto her by the way, and said, Go to, I pray thee, let me come in unto thee; (for he knew not that she was his daughter in law.) And she said, What wilt thou give me, that thou mayest come in unto me?
Genesis 38:16 stands in chapters 37-44, the first part of the story of Joseph and his brethren, which presents Jacob as a loving but unwise father who made Joseph, the son of his favorite wife and the petted child of his old age, the object of special affection above his other sons. The surrounding account exposes the evils of plurality of wives in the jealousies that existed not only between Jacob's wives but between their families, out of which hatred grew in Joseph's brethren against him so that they first attempted to slay him and finally sold him as a slave into Egypt, showing the sad fruits of Jacob's having more than one wife in low standards of morality and crime. The verse describes Judah turning aside to Tamar by the way and asking to come in to her because he did not know she was his daughter-in-law, she having unsettled herself and taken an unaccustomed path and apparel, showing that human knowledge and love can be estranged by ignorance and forgetfulness, since time, place, speech, or apparel can hide one person from another. It belongs to the account of Judah's sin with Tamar, who acted as a harlot with her father-in-law, an account that exposes sin so that it may be shunned rather than indulged or excused, and that reveals God's love, mercy, and power as the remedy.
From this encounter Pharez was born, and Pharez was an ancestor of Christ according to the flesh, so the verse is part of the account of Christ's human ancestry, which included people marked by human weakness, sin, and fallenness, with Tamar named among his ancestors in Matthew's genealogy. That sinful birth, together with Jacob's selfish, crafty, and deceitful disposition passed to his sons, Rahab the unenlightened heathen, and the sin and idolatry of Solomon, Rehoboam, Abijah, Jehoram, Ahaz, Manasseh, Amon, and other kings of Judah, proves the human line from which Christ sprang tended to concentrate in him all the weaknesses of humanity. Although his mother was pure and godly, his human nature was therefore more subject to the infirmities of the flesh and to sinful tendencies than if he had been born before the race had deteriorated physically and morally.
Christ's coming through such fallen ancestry and taking sinful flesh was not accidental but a necessary part of the plan of redemption, because only by taking the flesh that brings death and by suffering temptation could he die and sympathize with and aid tempted men. His family history including fallen people offers hope to the fallen. By contrast with human ignorance, the verse proves the Lord knows who are his, for time, place, speech, or apparel cannot obscure or darken his eye or ear, and he discerns and names his own everywhere.