John Gill Commentary 1 Chronicles 2

Ver. 1,2 These are the sons of Israel
Or Jacob, the other 1 Chronicles 2:2

(See Gill on 1 Chronicles 2:1).

You shall also take one ram
One of the two he was bid to take, (Exodus 29:1) ;

and Aaron and his sons shall put their hands upon the head of the ram ;
confessing their sins, acknowledging their guilt, and by this act transferring the same to the ram, which was to be a burnt offering, and was typical of the imputation of sin to Christ, as before observed.

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 38:2Genesis 38:12) ,

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, (Genesis 38:7Genesis 38:10) .

And Tamar his daughter in law bore him Pharez and Zerah
Through incest; they were twins, (Genesis 38:27–30) all the sons of Judah were five; who are before mentioned by name.

The sons of Pharez
One of the above twins, born to Judah:

Hezron and Hamul ;
see (Genesis 46:12) .