2 Chronicles - Chapter 21

We read here of one of the bad kings of Judah:

"But Jehoram followed the example of the kings of Israel and was as wicked as King Ahab, for he had married one of Ahab’s daughters. So Jehoram did what was evil in the Lord’s sight. But the Lord did not want to destroy David’s dynasty, for he had made a covenant with David and promised that his descendants would continue to rule, shining like a lamp forever."

To be described as being as wicked as King Ahab in Israel is a severe indictment.  Ahab was one of the most evil of Israel's kings.  However, God's treatment of Jehoram's line is different from that of Ahab's.  This is not because either of them was more or less deserving of judgment.  Rather, it is because God has made a promise to David that his descendants would continue to rule, and be a shining lamp forever.  Jesus was the descendant from Jehoram (he is listed in the genealogy in Matthew 1) who would be the shining lamp - the light of the light of the world - forever.