Here are the two passages for those unfamiliar with the issue:
2 Kings 8:26 Two and twenty years old was Ahaziah when he began to reign; and he reigned one year in Jerusalem. And his mother's name was Athaliah, the daughter of Omri king of Israel.
2 Chronicles 22:2 Forty and two years old was Ahaziah when he began to reign, and he reigned one year in Jerusalem. His mother's name also was Athaliah the daughter of Omri.
It's plain from the other details that these are talking about the same person.
The second text says plainly, "Forty and two years old". It does not say, "Forty and two years since (some other event)". Nowhere else in Scripture is the phrase, "x years old" used to mean something other than the number of years since a person's birth. Nobody reading the text would interpret it as anything other than a passage of time from the person's birth. If someone did say something like, "I was born in 1960; in 1970 I was 25 years old since the end of World War II", people would wonder at that person's intelligence and sanity.
While you can account for the numbers from a study of other passages, you cannot account for the wording without this convoluted and ridiculous explanation. You have to reject the plain text, and insert a comically nonsensical explanation, in order to defend your belief in the "perfection" of the KJV text.
Just admit defeat... the KJV is not perfect. Your life won't end, and since you lean on the faith of Christ and not your own, your relationship with God won't suffer.
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Jehu was appointed by God to cut off the house of Ahab. Ahab was the king of Israel, not of Judah. But Ahaziah was related to Ahab by marriage because his father Jehoram who "walked in the way of the kings of Israel, like as did the house of Ahab: FOR HE HAD THE DAUGHTER OF AHAB TO WIFE: and he wrought that which was evil in the eyes of the LORD" 2 Chronicles 21:6.
Likewise in 2 Kings 8:16-18 we read of Jehoram, the father of Ahaziah, that "he walked in the way of the kings of Israel, AS DID THE HOUSE OF AHAB: FOR THE DAUGHTER OF AHAB WAS HIS WIFE: and he did evil in the sight of the LORD."
And of his son Ahaziah, just a few verses later in 2 Kings 8:26-27 we read: "Two and twenty years old was Ahaziah when he began to reign; and he reigned one year in Jerusalem. And his mother's name was Athaliah, THE DAUGHTER OF OMRI (father of Ahab) king of Israel. And HE WALKED IN THE WAY OF THE HOUSE OF AHAB, and did evil in the sight of the LORD, AS DID THE HOUSE OF AHAB; FOR
HE WAS SON IN LAW OF THE HOUSE OF AHAB." Here we clearly see that Ahaziah is considered by God to be related to the house of Ahab and he walked in the way of the house of Ahab.
In 2 Chronicles 22:7 we read: "And
the destruction of Ahaziah was of God by coming to Joram: for when he was come, he went out with Jehoram against JEHU the son of Nimshi,
WHOM THE LORD HAD ANOINTED TO CUT OFF THE HOUSE OF AHAB."
To repeat, Ahaziah was son-in-law of the house of Ahab. 2 Kings 8:26 -27 "Two and twenty years old was Ahaziah when he began to reign: and he reigned one year in Jerusalem. And his mother's name was Athaliah, THE DAUGHTER (grand-daughter) OF OMRI KING OF ISRAEL. And HE WALKED IN THE WAY OF THE HOUSE OF AHAB, and did evil in the sight of the LORD, as did the house of Ahab: FOR HE WAS THE SON IN LAW OF THE HOUSE OF AHAB." Ahaziah is counted as a son-in-law to Ahab, even though it was his father who had married into the house of Ahab, and not Ahaziah himself.
Ahaziah was thus related by marriage to the house of Ahab through the marriage of his father with Athaliah the daughter of Ahab.
When it says in 2 Chronicles 22:2 that Ahaziah was 42 years old when he began to reign, this refers to his age as the last member of the reigning dynasty of the house of Ahab. Ahaziah could not have been 42 years old biologically, because his father was only 40 years old when Ahaziah became king (See 2 Chron. 21:20 - 2 Chron. 22:2 ). "Jehoram (the father of Ahaziah) was thirty and two years old when he began to reign, and he reigned in Jerusalem eight years, and departed without being desired...and the inhabitants of Jerusalem made Ahaziah his youngest son king in his stead...Forty and two years old was Ahaziah when he began to reign". For a man to become a father at the age of 18 is very likely, but for a son to be born two years earlier than his father is not.
The house of Ahab began, of course, with Ahab who reigned for 22 years and his son Jehoram was in his twelfth and final year at the time Ahaziah began to reign. 22 + 12 = 34. This would be the house of Ahab on the king's of Israel side.
When we look at the house of Ahab on the king's of Judah side and we come up with an additional 8 years reign as king on the part of Jehoram, Ahaziah's father. Jehoram "walked in the way of the kings of Israel, LIKE AS DID THE HOUSE OF AHAB: FOR HE HAD THE DAUGHTER OF AHAB TO WIFE: and he wrought that which was evil in the eyes of the LORD" 2 Chronicles 21:6.
22 + 12 + 8 = 42. This is the age of Ahaziah as a the youngest and most recent member of the extended reign of the house of Ahab over both Israel and Judah.
Ahab's other son, Ahaziah, who reigned for 2 years before Jehoram, does not come into consideration because his two year reign was overlapped on both sides by that of his father and of his brother. So the actual number of years the house of Ahab is in power is not affected or changed by his two year reign - his first year as co-regent to his father Ahab, and the second by his brother Jehoram, kings of Israel. The actual number of years the house of Ahab is in power is 42 years when we finally get to Ahaziah king of Judah, who himself was son in law of the house of Ahab and walked in the evil ways of the house of Ahab.
The two years of Ahaziah, Ahab's son, are overlapped on one side by Ahab his father and on the other by Jehoram his brother. 1 Kings 22:41 tells us that "Jehosaphat the son of Asa began to reign over Judah in the fourth year of Ahab king of Israel." Ahab reigned for 22 years, so at the time Jehosaphat begins to reign, Ahab has 18 more years to go as king of Israel.
When Ahab goes out to battle the Syrians, his son Ahaziah is made co-regent and remains in Samaria while his father goes to battle. 1 Kings 22:51 tells us "Ahaziah the son of Ahab began to reign over Israel in Samaria the seventeenth year of Jehoshaphat king of Judah, and reigned two years over Israel."
The 17th year of Jehoshaphat would overlap Ahab's 22nd and final year. Ahab dies in battle. So Ahaziah, his son, continues to reign in Samaria. However this same Ahaziah soon falls down through a lattice in his upper chamber and was sick with a disease that finally killed him.(See 2 Kings 1:2)
2 Kings 3:1 tells us: "Now Jehoram the son of Ahab began to reign over Israel in Samaria the eighteenth year of Jehoshaphat king of Judah, and reigned twelve years." Notice that Ahaziah (Ahab's son) began to reign in Jehoshaphat's 17th year, reigns 2 years, and Jehoram begins to reign in Jehoshaphat's 18th year.
We see that Ahaziah was co-regent to his father Ahab for one year and Jehoram, his brother, was co-regent to Ahaziah for one year during his sickness. Looked at in this way, his two year reign is overlapped by both that of his father and of his brother. We are left then with the 22 years of Ahab, 12 years of Jehoram of Ahab and the additional 8 years of Jehoram of Judah which again totals 42 years of reign till the time of Ahaziah of Judah.
Ahab's reign of 22 years does not overlap the 12 years of his son Jehoram. Likewise the one year of Ahaziah, king of Judah, does not overlap the reign of his father Jehoram. 2 Chronicles tells us that the band of men that came with the Arabians had slain all the eldest sons, so the only one left to sit on the throne was the youngest son, Ahaziah.
The house of Ahab was then cut off by Jehu when he killed both Jehoram of Israel and Ahaziah of Judah. Athaliah, that wicked queen, destroyed the rest of the seed royal of the house of Judah, except the baby Joash who was stolen away and hid for six years while Athaliah reigned. The continuous reign of successive "sons" (including son in law) of the house of Ahab ceased with the death of Jehoram and Ahaziah.
The central issue in all this is simply - How long was the combined reign of "the house of Ahab" over the two kingdoms of Israel and Judah? The answer is 42 years when Ahaziah began to reign. There is no error in either the Hebrew texts nor in all the Reformation bibles and many others even in modern times that tell us that Ahaziah was 42 years old when he began to reign.
Ahaziah was 42 years old as the final member of the house of Ahab, but only 22 years old physically as a son of Jehoram.