Abigail was the mother of Amasa, whose father was Jether the Ishmaelite.
Samuel calls him Ithra an Israelite, but that makes no sense; why mark a man as Israelite in David's day when nearly all were? The Septuagint reads Jetra the Jezreelite, which fits better. A woman marrying outside her tribe was rare enough to merit notice, and his being from Jezreel explains why the text names it.
AI summary
The twelve sons of Jacob descended through all Scripture, yet several of them were much blemished in character. But the covenant was entailed on their seed by free grace alone, not works, else any man might boast. The tribe of Judah, most praised and increased, produced both the vile and the virtuous in one line; Christ Himself, the top branch of that tree, grew from roots that held Achan the troubler and Tamar the woman wronged.
AI summary
Commenting on 1 Chronicles 2:1-17
Zeruiah's sons became the great warriors of David's reign, Abishai, Joab, Asahel, and her name endures in Scripture because her sons were more famous than their absent father. Abigail, David's half-sister through Nahash, bore Amasa, the captain whose name is bound up with Absalom's rebellion.
AI summary
Commenting on 1 Chronicles 2:16-17