1 Chronicles 2:3

“The sons of Judah, etc.] The genealogy begins with him, though the fourth son of Jacob; because, as Kimchi says, this book treats chiefly of the kings of Judah; but rather not only because Jesse and David sprang from him, but also the King Messiah: Er, and Onan, and Shelah, which three were born unto him of the daughter of Shua the Canaanitess; (see <013802>Genesis 38:2,12), and Er, the firstborn of Judah, was evil in the sight of the Lord; because he did that which was evil: and he slew him; he died by the immediate hand of God, and so his brother Onan, being wicked also, (<013807>Genesis 38:7,10).”

“Judah - Whom he puts first, because the best part of the right of the firstborn, namely, the dominion, was conferred upon him, Gen 49:8, and because the Messiah was to come out of his loins. 1 Chronicles 2:6”

“2:3–4:23 While the genealogies present the entire people of Israel (2:1-2), David’s ancestors in the tribe of Judah receive priority. 2:3-8 The genealogy of Judah is as comprehensive as possible, recording peripheral material as the background to the main line of David’s ancestors. Cp. Gen 46:12. 2:3 Er and Onan, the first two sons of Judah, were destroyed because of their sin (Gen 38:6-10). The descendants of Shelah are listed as an appendix at the end of the genealogies of Judah (1 Chr 4:21-23).”

“and: Ch1 9:5; Gen 38:2-10, Gen 46:12; Num 26:19 1 Chronicles 2:4”

“The sons of Judah and of Pharez, Ch1 2:3.f. - The five sons of Judah are given according to Gen 38, as the remark on Er which is quoted from Gen 38:7 of that chapter shows, while the names of the five sons are to be found also in Gen 46:12. The two sons of Pharez are according to Gen 46:12, cf. Num 26:21. 1 Chronicles 2:6”