Jamieson, Fausset and Brown on 1 Samuel 25:39-42

39-42. the Lord hath returned the wickedness of Nabal upon his own head--If this was an expression of pleasure, and David's vindictive feelings were gratified by the intelligence of Nabal's death, it was an instance of human infirmity which we may lament; but perhaps he referred to the unmerited reproach (1Sa 25:10, 11), and the contempt of God implied in it.

David sent and communed with Abigail, to take her to wife--This unceremonious proceeding was quite in the style of Eastern monarchs, who no sooner take a fancy for a lady than they despatch a messenger to intimate their royal wishes that she should henceforth reside in the palace; and her duty is implicitly to obey. David's conduct shows that the manners of the Eastern nations were already imitated by the great men in Israel; and that the morality of the times which God permitted, gave its sanction to the practice of polygamy. His marriage with Abigail brought him a rich estate.