1 Chronicles 2:8

For the family history of Zerah, compare Joshua 7:1, 17; 1 Kings 4:31 (Mahol might be another name for Zerah).

The genealogy of Judah is detailed, including background information on David's ancestors. Compare Genesis 46:12.

the sons of Carmi--He was the son of Zimri, or Zabdi, as he is called (Jos 7:1).

Achar--or Achan (Jos 7:1). This variety in the form of the name is with great propriety used here, since Achar means "troubler."

Here is, I. The family of Jacob. His twelve sons are here named, that illustrious number so often celebrated almost throughout the whole Bible, from the first to the last book of it. At every turn we meet with the twelve tribes that descended from these twelve patriarchs. The personal character of several of them was none of the best (the first four were much blemished), and yet the covenant was entailed on their seed; for it was of grace, free grace, that it was said, Jacob have I loved - not of works, lest any man should boast.
II. The family of Judah. That tribe was most praised, most increased, and most dignified, of any of the tribes, and therefore the genealogy of it is the first and largest of them all. In the account here given of the first branches of that illustrious tree, of which Christ was to be the top branch, we meet, 1. With some that were very bad. Here is Er, Judah's eldest son, that was evil in the sight of the Lord, and was cut off, in the beginning of his days, by a stroke of divine vengeance: The Lord slew him, Ch1 2:3. His next brother, Onan, was no better, and fared no better. Here is Tamar, with whom Judah, her father-in-law, committed incest, Ch1 2:4. And here is Achan, called Achar - a troubler, that troubled Israel by taking of the accursed thing, Ch1 2:7. Note, The best and most honourable families may have those belonging to them that are blemishes. 2. With some that were very wise and good, as Heman and Ethan, Calcol and Dara, who were not perhaps the immediate sons of Zerah, but descendants from him, and are named because they were the glory of their father's house; for, when the Holy Ghost would magnify the wisdom of Solomon, he declares him wiser than these four men, who, though the sons of Mahol, are called Ezrahites, from Zerah, Kg1 4:31. That four brothers should be eminent for wisdom and grace was a rare thing. 3. With some that were very great, as Nahshon, who was prince of the tribe of Judah when the camp of Israel was formed in the wilderness, and so led the van in that glorious march, and Salman, or Salmon, who was in that post of honour when they entered into Canaan, Ch1 2:10, Ch1 2:11.
III. The family of Jesse, of which a particularly account is kept for the sake of David, and the Son of David, who is a rod out of the stem of Jesse, Isa 11:1. Hence it appears that David was a seventh son, and that his three great commanders, Joab, Abishai, and Asahel, were the sons of one of his sisters, and Amasa of another. Three of the four went down slain to the pit, though they were the terror of the mighty.

Five of them in all - "These were all chief men; and on them the spirit of prophecy rested." - T.

And the sons of Ethan; Azariah. Including his posterity, see Genesis 46:23, the posterity of the other three sons of Zerah are not mentioned, either because the writer could not find the genealogy of them, as Kimchi; or rather, as he thinks, he cuts short the genealogy of Zerah, because the kingdom did not proceed from him, and returns to the genealogy of Hezron, from whence it did, or perhaps they had no children.

And Jesse begat his firstborn Eliab, and Abinadab the second, and Shimma the third, Nathanael the fourth, Raddai the fifth, Ozem the sixth, David the seventh. But Jesse had eight sons, Sa1 16:10, one of them therefore is not reckoned, either because he was by another woman, and the writer only mentions those that were of the same mother with David; this is the opinion of Aben Ezra and Kimchi; some say he was dead before David came to the kingdom; Kimchi mentions a Midrash, or exposition of theirs, according to which his name was Elihu, and was younger than David, who is mentioned in Ch1 27:18, and Jarchi observes, that the writer, having found the pearl (David), reckons not the eighth son Elihu, though the Syriac and Arabic versions have inserted him in this order, "Elihu the seventh, David the eighth"; some take the eighth to be a grandson of Jesse, Jonathan the son of Shimea, Sa2 21:21 the third son of Jesse, here called Shimma, as he is Shammah, Sa1 16:9.
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1 Chronicles 2:16

ch1 2:16
ch1 2:16
ch1 2:16Whose sisters were Zeruiah and Abigail..... That is, sisters of David:

and the sons of Zeruiah; Abishai, and Joab, and Asahel, three; all valiant men and captains in David's army; their father's name is nowhere mentioned.