The sons of Judah,.... 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 Genesis 38:2,
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, Genesis 38:7.