2 Samuel 5:13

David took him more concubines and wives This may well be reckoned among David's miscarriages, the multiplication of wives being expressly forbidden to the kings of Israel, Deuteronomy 17:17. It may however be observed, perhaps in extenuation of this fault of David, that it has always been looked upon as a piece of political wisdom in princes to endeavour to have many children; that by matching them into potent families, they might strengthen their interest, and have the more supporters of their authority. And this seems to have been the reason why David took so many wives. Some of his first wives had no children, and he was induced to take others that he might obtain an issue, enlarge his family, and thereby strengthen his interest. But the many wives and concubines he took did not preserve him from coveting his neighbour's wife. On the contrary, they inclined him to it; for men who have once broken the fence, will wander carelessly.