Jacob 1:15

And now it came to pass that the people of Nephi, under the reign of the second king, began to grow hard in their hearts, and indulge themselves somewhat in wicked practices, such as like unto David of Old, desiring many wives and concubines, and also Solomon, his son;

Under the second king, the Nephites began to have hard hearts. They started doing bad things. Like King David long ago, they wanted many wives. Solomon his son did the same thing.

During the second king’s reign, Nephi’s people started to harden their hearts. They slipped into sinful behavior—wanting multiple wives and concubines, just like David and his son Solomon back in the old days.