Question: "What is the significance of the forty-two months in Revelation 13:5?"
Answer: In Revelation 13 John records a vision of a beast with ten horns and seven heads. According to Revelation 13:5, the beast will be given authority for forty-two months (three and a half years) and will rule over the whole earth during that time (Revelation 13:7–8). Earlier in the book of Revelation, John recorded someone saying that the holy city (Jerusalem) would be trampled under foot by the nations for forty-two months (Revelation 11:2). Two prophets of God would prophesy for 1,260 days—also equal to forty-two months on the 360-day lunar calendar that Israel used (Revelation 11:3).
The significance of forty-two months in Revelation 13:5 and other passages in Revelation is first explained in Daniel 9 and then again in Matthew 24. In Daniel 9 Daniel is reading Scripture and praying that God will restore Israel from captivity according to what God had promised (Daniel 9:2–3). Even while Daniel was speaking, God sent the angel Gabriel to assure Daniel that God would keep His word and would not forsake Israel (Daniel 9:20–23). Gabriel explained that there would be a prophetic calendar of seventy sevens, or 490 years (Daniel 9:24). The calendar would commence with a decree to rebuild the city of Jerusalem (Daniel 9:25). That decree is recorded in Nehemiah 2:8.
After sixty-nine sevens, or 483 years from that decree, the Messiah would be cut off and the people of the prince to come would destroy the city and the temple (Daniel 9:26a). Just as Gabriel said, the Messiah was crucified after the 483 years, and a few decades after that, the Romans destroyed the temple and the city of Jerusalem (in AD 70). From that point to the end or completion, there would be wars and desolations (Daniel 9:26b). It seems that the 490-year calendar is paused during this time. The calendar will restart with the (Roman) prince making a covenant with “the many” (often a reference in Hebrew prophecy to Israel) for one seven, or seven years. In the middle of that time period, the prince will break his covenant. That will leave forty-two months of desolation to complete the prophetic calendar (Daniel 9:27). That last forty-two months or three and a half years will be dominated by one who makes desolate. At the end of that time, he is made desolate himself.
In Matthew 24, in what has become known as the Olivet Discourse, Jesus explains to His disciples what the future will hold for Israel (Matthew 24:2–3). Jesus warns against false messiahs and that there will be wars and rumors of wars (Matthew 24:5–6). But these things would not be the end. There would be persecutions and difficulties for the disciples and all who would follow Jesus (Matthew 24:9; cp. 2 Timothy 3:12). But the good news of Jesus’ coming kingdom would be proclaimed in all the earth (Matthew 24:14). After that, the completion or the end will come. Jesus references “the abomination of desolation” as the beginning of a great tribulation unlike anything the world has seen before or would see after (Matthew 24:15, 21, NKJV). This means that, during the second half of the final seven years, the tribulation will be even more severe than in the first half. Jesus divides this time period into two forty-two-month periods. He adds that the time of difficulty will be cut short—if it were not, no one would survive (Matthew 24:22). Trouble will last the entire eighty-four months (seven years), but the worst events are reserved for the final forty-two months. After that tribulation and great tribulation, Jesus will come again in great glory (Matthew 24:29–30). With Him will be all those who have believed in Him and who are already in heaven (Matthew 24:31).
The book of Revelation unveils many details especially of the final seven years (or eighty-four months) of God’s prophetic calendar, leading up to the return of Jesus Christ the King. Even though evil is given dominion for forty-two months, the clock will eventually run out, and Jesus will triumph. This message was an encouragement to Daniel and to Jesus’ disciples. It should also encourage us and challenge us to make the most of the time we have been given. As Jesus said, He is coming suddenly and wants all to heed the prophetic words in Revelation (Revelation 22:7). Jesus will come back to the earth victorious over evil (Revelation 19:13–19), even though He will allow evil to rule for forty-two months.