How we cite our quotes:
Quote #4
[King Abijah] said, "Listen to me, Jeroboam and all Israel! Do you not know that the Lord God of Israel gave the kingship over Israel forever to David and his sons by a covenant of salt? Yet Jeroboam son of Nebat, a servant of Solomon son of David, rose up and rebelled against his lord; and certain worthless scoundrels gathered around him and defied Rehoboam son of Solomon, when Rehoboam was young and irresolute and could not withstand them. And now you think that you can withstand the kingdom of the Lord in the hand of the sons of David?" (2 Chronicles 13:4-8, NRSV)
[King Abijah] said, Hear me, thou Jeroboam, and all Israel; Ought ye not to know that the Lord God of Israel gave the kingdom over Israel to David for ever, even to him and to his sons by a covenant of salt? Yet Jeroboam the son of Nebat, the servant of Solomon the son of David, is risen up, and hath rebelled against his lord. And there are gathered unto him vain men, the children of Belial, and have strengthened themselves against Rehoboam the son of Solomon, when Rehoboam was young and tenderhearted, and could not withstand them. And now ye think to withstand the kingdom of the Lord in the hand of the sons of David. (2 Chronicles 13:4-8, KJV)
Among the Northern Kingdom's other sins is their refusal to accept God's choice of kings. Even though we're given a reason for Jeroboam's rebellion (Rehoboam increasing the work burdens and generally acting like a heartless jerk), Jeroboam and his followers are still seen as scoundrels. Like it or not, covenant of salt is a covenant of salt. BTW, it's been suggested that since salt is a preservative, it symbolized the long-lasting nature of a covenant. (Source)
Quote #5
Have you not driven out the priests of the Lord, the descendants of Aaron, and the Levites, and made priests for yourselves like the peoples of other lands? […] But as for us, the Lord is our God, and we have not abandoned him. We have priests ministering to the Lord who are descendants of Aaron, and Levites for their service. (2 Chronicles 13:9-10, NRSV)
Have ye not cast out the priests of the Lord, the sons of Aaron, and the Levites, and have made you priests after the manner of the nations of other lands? […] But as for us, the Lord is our God, and we have not forsaken him; and the priests, which minister unto the Lord, are the sons of Aaron, and the Levites wait upon their business. (2 Chronicles 13:9-10, KJV)
The priests in Israel don't come from the right family either. According to Exodus, only Aaron's sons and grandsons (and so on) could serve as high priests. No substitutions. It's the same with the Levites. There were Temple-related activities that only Levites were permitted to do, and using non-Levites to do those things could lead to trouble. These were very rigid bloodline rules.
Quote #6
Jehoshaphat slept with his ancestors and was buried with his ancestors in the city of David; his son Jehoram succeeded him. He had brothers, the sons of Jehoshaphat: Azariah, Jehiel, Zechariah, Azariah, Michael, and Shephatiah; all these were the sons of King Jehoshaphat of Judah. Their father gave them many gifts, of silver, gold, and valuable possessions, together with fortified cities in Judah; but he gave the kingdom to Jehoram, because he was the firstborn. When Jehoram had ascended the throne of his father and was established, he put all his brothers to the sword, and also some of the officials of Israel. (2 Chronicles 21:1-4, NRSV)
Jehoshaphat slept with his fathers, and was buried with his fathers in the city of David. And Jehoram his son reigned in his stead. And he had brethren the sons of Jehoshaphat, Azariah, and Jehiel, and Zechariah, and Azariah, and Michael, and Shephatiah: all these were the sons of Jehoshaphat king of Israel. And their father gave them great gifts of silver, and of gold, and of precious things, with fenced cities in Judah: but the kingdom gave he to Jehoram; because he was the firstborn. Now when Jehoram was risen up to the kingdom of his father, he strengthened himself, and slew all his brethren with the sword, and divers also of the princes of Israel. (2 Chronicles 21:1-4, KJV)
Apparently rules of family descent didn't mean you had to like your family. Once the requirement was fulfilled—i.e., a Davidic king was on the throne—the other brothers are dispatched. This obviously wasn't what Jehoshaphat had in mind because he made bequests to all his sons. The favored firstborn is a theme throughout the Bible, but it's just as often turned upside-down, like when Jacob stole the birthright from Isaac or when Joseph ended up as way more powerful than all his older brothers. Some of the Davidic kings are firstborns and others aren't, for a variety of reasons.