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.

Wesley's Notes

38:28 It should seem the birth was hard to the mother, by which she was corrected for her sin: the children also, like Jacob and Esau, struggled for the birth - right, and Pharez who got it, is ever named first, and from him Christ descended. He had his name from his breaking forth before his brother; this breach be upon thee - The Jews, as Zarah, bid fair for the birth - right, and were marked with a scarlet thread, as those that come out first; but the Gentiles, like Pharez, or a son of violence got the start of them, by that violence which the kingdom of heaven suffers, and attained to the righteousness which the Jews came short of: yet when the fulness of time is come, all Israel shall be saved. Both these sons are named in the genealogy of our Saviour, Mt 1:3, to perpetuate the story, as an instance of the humiliation of our Lord Jesus.

Matthew Henry's Concise Commentary

38:1-30 The profligate conduct of Judah and his family. - This chapter gives an account of Judah and his family, and such an account it is, that it seems a wonder that of all Jacob's sons, our Lord should spring out of Judah, Heb 7:14. But God will show that his choice is of grace and not of merit, and that Christ came into the world to save sinners, even the chief. Also, that the worthiness of Christ is of himself, and not from his ancestors. How little reason had the Jews, who were so called from this Judah, to boast as they did, Joh 8:41. What awful examples the Lord proclaims in his punishments, of his utter displeasure at sin! Let us seek grace from God to avoid every appearance of sin. And let that state of humbleness to which Jesus submitted, when he came to put away sin by the sacrifice of himself, in appointing such characters as those here recorded, to be his ancestors, endear the Redeemer to our hearts.