After David performed a census of Israel and Judah, the Lord gave David the opportunity to choose one of three possible judgments that would befall his nation. However, at first glance, the two passages that record these options seem to contradict each other.
So Gad came to David and told him; and he said to him, “Shall seven years of famine come to you in your land? Or shall you flee three months before your enemies, while they pursue you? Or shall there be three days’ plague in your land? Now consider and see what answer I should take back to Him who sent me.” (2 Samuel 24:13)
So Gad came to David and said to him, “Thus says the Lord: ‘Choose for yourself, either three years of famine, or three months to be defeated by your foes with the sword of your enemies overtaking you, or else for three days the sword of the Lord—the plague in the land, with the angel of the Lord destroying throughout all the territory of Israel.’ Now consider what answer I should take back to Him who sent me.” (1 Chronicles 21:11–12)
At first glance, it does appear that the above verses contain an inconsistency: one passage offers a choice of three years famine, while the other seemingly offers seven years of famine.
Regarding 2 Samuel 24:13, many English translations follow the Septuagint by using “three” in place of “seven.” If this were the original reading, then we would have an example of a copyist error. It is possible for copyist errors to have crept into some documents, and since the doctrine of inerrancy only applies to the original manuscripts, such errors would have no impact on this crucial doctrine.
Not surprisingly, some critics of biblical authority present this apparent incongruity as evidence confirming their pre-committed disbelief in the inerrancy and divine inspiration of Scripture. Others cite this to justify their claim that modern copies of the biblical texts insufficiently represent the original manuscripts.
In reality, these accusations of corruption are unwarranted, and there are at least a couple of plausible solutions that do not appeal to a copyist error.
The key lies in understanding the greater context of the account. Let us first consider a verse that precedes the account in 2 Samuel:
Now there was a famine in the days of David for three years, year after year; and David inquired of the Lord. And the Lord answered, “It is because of Saul and his bloodthirsty house, because he killed the Gibeonites.” (2 Samuel 21:1)
Clearly, Israel had already experienced three years
of famine before David numbered the people of Israel and
Judah—for reasons unrelated to the situation in
question.
2 Samuel 24:1–7 record the initiation of the
census, but we find in verse 8 that “when
they had gone through all the land, they came to
Jerusalem at the end of nine months and twenty days.
”
So according to the text, numbering the people was nearly a year-long process, and there is no clear indication that God had suspended the initial three-year famine prior to the events in chapter 24. Now if God had combined three additional years of famine (1 Chronicles 21:12) with the three years of initial famine, and a possible intervening year while the census was conducted, the resulting overall famine would have totaled about seven years (2 Samuel 24:13).
Some Christians have proposed another solution. They claim that these two passages describe the prophet Gad confronting David on two different occasions. According to this view, the “seven year” proposal was initially given four years prior to the “three year” proposal. Thus, the prophet would have confronted David and given him a few years to mull over his decision. During that time, David had repented of his actions so God reduced the time of punishment—something God definitely has the authority to do. A problem with this view is that if God reduced the seven years to three years because of David’s repentance, then why didn’t He reduce the length of the other options as well? So while this solution may seem less likely, it still provides another reasonable explanation.
The important thing to realize is that regardless of which solution we choose, the result is the same. The accusation of contradiction evaporates—all without declaring the text in error. In conclusion, these Scriptures not only are compatible, but also work together to provide additional details on this particular event.
http://www.answersingenesis.org/articles/2012/08/14/contradictions-famine-three-seven-years