Gumby's statement that John the baptist's ministry lasted six months is based on JW chronology, not anything specifically stated in scripture.
JWs say Jesus was born in 2 BC. They also say that Jesus was thirty years old when he began his ministry, though the Bible does not exactly say that. The Bible does say that John baptized Jesus in "the 15th year of Tiberius Caesar," which historians tell us was AD 29. The Bible also says that John the baptist was about six months older than Jesus. And it tells us that Jewish men always waited until turning thirty before beginning their public ministry. So then, if all of the above things were true, John's ministry could not have been any longer than six months.
But all of these things are not necessarily true. For instance, most New Testament historians date the birth of Christ to about the year 5 BC, not 2 BC. If they are correct, John the baptist being about six months older than Jesus would have turned thirty in AD 26, and could have preached for more than three years before he baptized Jesus in AD 29.
I believe the solution to this problem can be found by taking a closer look at the word Luke used in Luke 3:23 which has been widely translated as "about." That Greek word is "hosei." Bible historians who date the birth of Christ to about 5 BC believe that Luke's saying that Jesus was "about 30" in 29 AD allows room for us to understand that Jesus could have been two or three years past 30 when he began his ministry. They also tell us that "hosei," the word Luke chose to use before the number 30, actually indicates a greater indefiniteness than the Greek word "hos" which Luke used elsewhere to convey the thought that the number he mentioned may not have been exactly as stated. And, Greek lexicons indicate that "hosei" may have actually been used here by Luke to mean more than just "about." They show that Luke may have used this Greek word to say that Jesus was then beginning his ministry "as if" he were 30, "as though" he were 30, "like" he was 30 or since he "had already been" 30. Why? Because Jewish men usually began their service to God at age 30 and were not permitted to do so before that age.
Those who believe that Christ was born some time after 4 BC argue against such understandings. However, I have found what I consider to be strong biblical evidence which clearly shows that Christ must have been born in the year 5 BC.
For I believe that the Bible very clearly indicates that John the baptist began his ministry as "a voice of one calling in the desert, 'Prepare the way of the Lord,' " (Luke 3:4 ) three and a half years before Jesus began his ministry. If this is true, and Jesus began his ministry in the fall of 29 AD, as most New Testament historians tell us, then John must have begun his ministry, preparing the people of Israel for the coming of their Messiah, in the spring of 26 AD. And since John was a Levite, and Levites according to the Jewish law began their service to God after turning thirty years of age (Numbers 4:1-3, 21-23, 29-30, 34-35, 46-49), John must have been born no later than the spring of 5 BC.
The "strong biblical evidence" I refer to comes to light when we ask and answer the following questions: Why was John the baptist prophetically referred to as Elijah? (Malachi 4:5,6; Matt. 11:12-14; 17:10-13; Luke 1:17) Why was he compared to Elijah rather than some other prophet such as Elisha or Jeremiah or Isaiah or Ezekiel or Daniel or Zechariah or any one of Jehovah's many other prophets of years gone by? Though John denied that he really was Elijah (John 1:21), he clearly went to great lengths to copy part of Elijah's prophetic ministry. To make it quite plain exactly what he was doing, John even dressed like Elijah. (2 Kings 1:8; Matt. 3:4; Mark 1:6) Why?
I have found there is really only one way to answer these questions. The answers are found by studying the prophetic life of Elijah. Specifically, the part of his prophetic life which we read about in 1 Kings chapters 17 and 18. There we find that, during the reign of King Ahab, Elijah prophesied that in northern Israel there would "be neither dew nor rain in the next few years except by my word." (1 Kings 17:1) Elijah's prophecy proved true when a long drought followed causing a severe famine in the land. At the end of those "few years" Elijah introduced a long awaited and greatly needed shower of rain to Israel.
Nowhere in the Old Testament are we told exactly how many years passed before Elijah ushered in the rain Israel had so long been waiting for. However, the New Testament provides us with this information twice. First, in Luke 4:25, Jesus himself told us that, "In Elijah's time the sky was shut for three and a half years." Later James told us that, "Elijah was a man just like us. He prayed earnestly that it would not rain, and it did not rain on the land for three and a half years. Again he prayed and the heavens gave rain." (James 5:17,18)
Why does the New Testament tell us exactly how long Elijah served as God's prophet while the people of his land waited for rain? I believe it does so in order to provide us with the chronological information we need to determine the time of Christ's birth.
For just as Elijah served as a prophet of God for three and a half years while the people of Israel were longing for rain to come to their land, John the baptist prophesied "the coming of the Lord" while the people of Israel were longing for the Messianic rain to come to them. This Messianic "rain" was prophesied to come to Israel in the 72nd Psalm. There we read in part, "Endow the king with your justice, O God, the royal Son with your righteousness. He will judge your people in righteousness and your afflicted ones with justice. He will be like rain falling on a mown field, like showers watering the earth. All kings will bow down to him and all nations will serve him. All nations will be blessed through him and they will call him blessed." (Ps. 72: 1, 2, 6, 11, 17)
With this Messianic prophecy in mind, it seems clear why the New Testament informs us of exactly how long Elijah prophesied while waiting for rain to fall on Israel. Why? So we today can understand that the latter day "Elijah," John the baptist, prophesied "the coming of the Lord" for exactly three and a half years before he introduced the long awaited and greatly needed Messianic "rain" to the Jewish people. (John 1:29-31)
Now, no doubt some will ask, "Doesn't the Bible tell us that John the baptist began his ministry in 29 AD, 'in the fifteenth year of Tiberius Caesar'? And if it does, since Jesus also began his ministry in 29 AD, doesn't that prove that John's ministry could have only been about six months long, since it began in the same year that Christ also began his ministry?"
I believe the answer to both of these questions is, "No." The Bible does not tell us that John the Baptist began his ministry in "the fifteenth year of Tiberius Caesar" which was 29 AD. It only tell us that in that year "the word of God came to John the son of Zechariah in the desert." (Luke 3:1, 2) Now, the traditional thinking has been that "the word of God" there referred to instructed John to begin "calling in the desert, 'Prepare the way of the Lord.' " (Luke 3:4) The problem with this understanding is that it is only an assumption. And considering other information given to us in scripture, it does not appear to be a valid one.
I do not believe that Luke 3:1, 2 tells us that John the baptist began his ministry "in the fifteenth year of Tiberius Caesar," but rather that John's ministry culminated in that year with his baptism of Jesus Christ. By understanding Luke chapter three in this way we find that John did not necessarily begin his service to God in 29 AD. We also find that Luke chapter three does not limit the time John prepared the way for Christ to only a few months. Rather, it allows us to understand that John began his ministry three and a half years before introducing a greatly needed "rain" to Israel (Ps. 72: 1, 2, 6, 11, 17), just as Elijah had done before him. (1 Kings 17, 18)
With this understanding of Luke 3:1, 2 in mind, we can also appreciate why Luke so carefully recorded the time of the event he was then referring to, and by so doing attached such great importance to it. Because in Luke 3:1, 2 Luke was not telling us when John the baptist began his ministry. Rather, he was recording for posterity the exact time that Jesus Christ began the most important service to God and mankind that has ever been rendered.
To confirm this understanding is correct there is one more point that should be made. That is, that if Luke's words recorded in Luke 3:1,2 were intended to date the beginning of John the baptist's ministry, then Luke attached more historical significance to the ministry of John than he did to the ministry of Jesus Christ. For in Luke 3:1, 2, in an effort to help us accurately determine the time of the event he was there recording, Luke painstakingly listed seven different contemporary historical public figures by name, and five separate geographical regions which were controlled at the time by the five governmental officials on his list. If, as has been suggested, Luke 3:1, 2 is referring to the time John the baptist's ministry began, Luke went to great lengths to tell us the time John began his ministry but made no attempt at all in his gospel to tell us of the time when Christ's ministry began.
There is only one sensible explanation for Luke's seemingly confused sense of priority. That is, to understand that in Luke 3:1, 2, Luke was not recording the time when John the baptist began his ministry. Rather, as stated earlier, he was recording the time when Jesus Christ began his public service to God.
As a final thought in support of this understanding, I will point out that Luke tells us that in the fifteenth year of Tiberius Caesar, when "the word of God came to John" it came to him while he was already "in the desert." There John served God as "a voice crying in the wilderness, 'Prepare the way of the Lord.' " In other words, Luke 3:1, 2 tells us that when the word of God came to John, in the fifteenth year of Tiberius Caesar, John's ministry had already begun. And I believe all the facts from history and scripture combine to show that it had begun three and a half years earlier, in the spring of 26 AD. And if John began his ministry upon turning 30 years old, as all Levite men did, and if he first served as a priest for a brief but respectable period of time, as all Levite men were required to do, then we can reasonably conclude that John was most likely born in the later part of 6 BC. And if we do, since John was about six months older than Jesus, we must also conclude that Jesus was most likely born in the early part of the year 5 BC.
And if John's ministry lasted three and a half years, it is certainly possible he may have been arrested more than once, though I don't believe that such an understanding is required in order to harmonize the Bible's historical accounts.