Why did John the Baptist exist? Did he have any purpose besides Baptizing Jesus?

Besides that, what is John the Baptist's contribution/significance/utility to Christianity?

Introduction:

To begin let me take this opportunity to congratulate the other posters preceding this element of the answer! It would be frivolous for me to take a chance to improve what has already been shared; and I humbly yield to the others discourse and factual presentation per se! However the answer that I would add as an attempt to unlock some of the elements about John the Baptist; that has been known for millennia and somewhat suppressed. As to that action I do not care to be overly contentious about the issue.

The following are a brief reference to answer the issue at hand!

Isaiah 48:16 (KJV)

17 Thus saith the LORD, thy Redeemer, the Holy One of Israel; I am the LORD thy God which teacheth thee to profit, which leadeth thee by the way that thou shouldest go.

John 14:6 (KJV)

6 Jesus saith unto him, I am the way, the truth, and the life: no man cometh unto the Father, but by me.

Problem Defined

Jeremiah 10:1-9 (KJV) 1 Hear ye the word which the LORD speaketh unto you, O house of Israel: 2 Thus saith the LORD, Learn not the way of the heathen, and be not dismayed at the signs of heaven; for the heathen are dismayed at them. 3 For the customs of the people are vain: for one cutteth a tree out of the forest, the work of the hands of the workman, with the axe. 4 They deck it with silver and with gold; they fasten it with nails and with hammers, that it move not. 5 They are upright as the palm tree, but speak not: they must needs be borne, because they cannot go. Be not afraid of them; for they cannot do evil, neither also is it in them to do good. 6 Forasmuch as there is none like unto thee, O LORD; thou art great, and thy name is great in might. 7 Who would not fear thee, O King of nations? for to thee doth it appertain: forasmuch as among all the wise men of the nations, and in all their kingdoms, there is none like unto thee. 8 But they are altogether brutish and foolish: the stock is a doctrine of vanities. 9 Silver spread into plates is brought from Tarshish, and gold from Uphaz, the work of the workman, and of the hands of the founder: blue and purple is their clothing: they are all the work of cunning men.

Answer:

The key begins earlier in the text at Matthew 3: 3, “… Prepare ye the way of the Lord, make his paths straight.” The emphasis was to bring Israel into alignment with their calling! The unique element of John The Baptist; that is demonstrable by scripture and scripture alone is, his birth sequence and coordination with the Birth of Jesus The Messiah! The facts of the birth sequence are based upon the calendars taught within Judaism and also in practice by Messianic groups worldwide, some call them completed Jews and I applaud them for finding their Messiah, there are variants

Again I do not care to be contentious about this but rather willing to share to the serious discerning student! The details are explosive on a global scale in geopolitics, economics and in the spiritual realm of contemporary Christianity; Protestant, Orthodoxy, Roman Catholic, Pentecostal, Charismatic it does not matter plus variant other Independent believers. Wars and persecution have been waged since the occurrence of those events. And I do not think this is the proper format to engage in this study, due to the fact there is a “we can’t handle the truth” policy!

Addendum: Due to the suggestion of a moderator, I will comply.

I make no change to the original post, other than applying bold to the simplicity of the answer and a variant clarifier to end of answer paragraph!

When the sincere discerning student of scripture truly desires to find the integrity to the submitted answer above; all extra biblical postulations must be set aside, to be dealt with at a later time. The student can then collate all aspects leading to the birth of John the Baptist. There will be a list of priestly order of Zachariah, his father, and their scheduled order in the Temple service, reference is I Chronicles 24. There will be applied from within The Law of Moses, concerning the sacrifices required of Elisabeth, his mother, concerning her uncleanness, reference is Leviticus 15:19-33. Then we must also understand that all priest were to perform their assigned duties during the Festivals set forth beginning in Exodus 23:14 & Deuteronomy 16:16. Furthermore; as restricting parameters we will apply boundaries to the calendar; by reference I Corinthians 4:6 “…not to think above that which is written…” & Galatians 4:4 “…made under the law…”! (To amplify the use of “made” some underlying translation use variants as follows; 1) to become, i.e. to come into existence, begin to be, receive being, 2) to come to pass, happen, 3) to arise, appear in history, come upon the stage, 4) to be made, finished! (KJV italics removed)

Now we begin to collate the events leading up to the meeting of Elisabeth and Mary the mother of Jesus The Messiah.

In order to save a lot of frustration; it would be easier to explain the details within a spread sheet format (this picture is worth 10,000s of words). I have used this for some time and thanks to software applications (excel) it is much simpler to edit, etc. We use legal size with landscape view (columns A-Q and 90 lines). Column A is widened 2-2 1/2” for reference & notes, column B will represent the pre-natal count for John the Baptist, column C is for the priestly order for service, column is D blank, columns E-K are for the enumerated calendar for this study, column L is blank, “COLUMN M” will be used for the prenatal count for Jesus The Messiah, columns N-Q will be for additional reference & notes some may be merged depending upon your personal preference, if you chose to continue (this mission is not impossible). Then we start by establishing the calendar to the Biblical format of lunar months (Gregorian calendar; solar and astrological elements do not apply!) Column E1-K1 begins and continues though the entire format (7 day week, down to line 90) and the Biblical lunar months alternate between 30 & 29 days respectively! I wish it could be set in a comma delimited format, however if you place each reference to the spread sheet as presented (column-line reference), simply check off each entry as you go through the explanation process.

Beginning at; A1 & A2, Levites on duty by course>>> - ref. I Chronicles 24, C1 = 1 (to enumerate down the column, the priestly order 1-24, N1= Exodus 12:2 “…beginning of months…”, A3 = Passover, C3 = ALL (all priest at 3 major festivals), A4 is Aviv / March-April, A9 = Luke 1:5-22 Abiyah / Zacariah (the father of John the Baptist in his normal rotation within the priestly order by course!) At A10 = Luke 1:23 (Pentecost or Weeks), C10 = ALL (festival requirement). At A12 = Leviticus 15:26, at C11 & 12 underline the priestly order numbers; began earlier (should be 9 &10) (to allow the guidelines set forth in reference as a variable within the calendar, Elisabeth separation for uncleanness). If it is in scripture it behooves the student to consider the facts! At A13 = Luke 1:24a / Luke 1:24b Elisabeth to hiding, A14 = begin prenatal count for John the Baptist>>> & at B14 = 1 (to begin enumeration down the column to the full term birth of JB), at A53 = Passover (full term birth of JB) & C53 = ALL (festival). At A52 = Luke 1:57-79, K52 should be 10 and bold, N52 = Lamb brought in on sabbath, A54 = JB circumcision (8th day), N54 = Luke 1:59, A61 = Pentecost, C61 = ALL (festival)! Note Zacariah does double duty back to back; on regular course and Pentecost!

If your brain is burning it will heal as this is absorbed and comprehended as, contrary to the traditions of men! We now need to correlate the meeting of Elisabeth, having been in hiding for 5 months, with Mary the mother of Jesus The Messiah! At A34 = Luke 1:24b (hidden 5 months), B34 should be 21, at A37 = Luke 1:26, A38 = Hanukkah (2nd feast of lights); this is the Ace in the hole Royal Flush and an unbeatable hand! At B38 should be 25, C38 = 7, N38 = Luke 1:27-39 dedication of her temple, A39= Luke 1:40-56, N39 = begin prenatal count for Jesus The Messiah, M39 = 1 to begin down column enumerations for full term birth of Jesus The Messiah! At A78 = Yom Kippur*, C78 = 1, E-K78 = 9-15, M78 = 40, N78 = Luke 2:7 HIS BIRTH, A79 = TABERNACLES (II Chronicles 6 & 7 as a comparative reference), C79 = ALL, E-K79 = 16-22, N79 = Luke 2:21 – HIS CIRCUMCISION, N84 = Luke 2:22 “His Dedication in Temple” ref. is LV 12:1-4! As an extra emphasis on this calendar we can now add an oversize right brace from O78 drawn down to O85 with point to right, then we can merge cells OPQ81 & 82 (in these merged cells enter in as large as possible and bold “Galatians 4:4”

I admit this ordeal sounds a tad rough or tedious however it does correspond with scripture! Do not forget to enter the other festivals and correlate the priestly numberings, the calendar days are important and need to be reconciled with scripture! (proof PDF available)

Isaiah 61:2 (KJV) 2 To proclaim the acceptable year of the LORD, and the day of vengeance of our God; to comfort all that mourn;

Luke 4:19-21 (KJV)
19 To preach the acceptable year of the Lord. 20 And he closed the book, and he gave it again to the minister, and sat down. And the eyes of all them that were in the synagogue were fastened on him. 21 And he began to say unto them, This day is this scripture fulfilled in your ears.

John the Baptist is a key to establishing; The Acceptable Year of The Lord!

As we read in Matthew 3:1-17, John's most important role was to announce the coming of Jesus and to baptise him, so if that was all there was to his life he could have died then and justified his existence. But John the Baptist had another purpose, which was to be fulfilled before he died. As the gospels note, John publicly criticised Herod Antipas for marrying Herodias, his brother's former wife, contrary to Jewish law.

Because of his criticism, John was arrested and placed in the prison tower of Macherus, east of the Dead Sea, then executed so as to prevent him from stirring up trouble among the Jews. Josephus places the marriage at the same time as, or shortly after, the death of Philip II, who he says died in the twentieth year of the reign of Tiberius (34 CE). John was revered by the Jews and admired for his principled stand against Antipas, with many believing that the Nabataean King Aretas' defeat of Antipas soon afterwards, in 36 CE, was divine retribution for the death of John.

Josephus, Antiquities of the Jews, 18.5.2: Now some of the Jews thought that the destruction of Herod's army came from God, and that very justly, as a punishment of what he did against John, that was called the Baptist: for Herod slew him, who was a good man, and commanded the Jews to exercise virtue, both as to righteousness towards one another, and piety towards God, and so to come to baptism

Ok, Luke goes the extent of not just introducing John but introduces his parents as well. This I think is very important as it implies the authority from which John himself might have received his ordination. Zechariah was a priest who got a specific word from God about his son John. In this way we can safely say that John had the role of publicly initiating Jesus into the ministry. Gabriel also informs Zechariah that through John many people's heart would be returned to the lord. So though Jesus did meet upon many whose hearts were quite hardened, we can still appreciate that it might have been a worse situation if John had not done what he did.

John continued the line of prophetic tradition which seemed to have been some how halted. He came as 'a voice' crying out in the wilderness. Indeed, God when he is ready to release his though looks for one who would be his voice and John was that voice.

His was the voice that prepared the way by urging people to prepare the way, almost like a manager of a great road construction. The way is being prepared as for a dignitary who is none other than the King of kings. Its interesting though that though they are being compelled to prepare the way for Jesus, it was Jesus who would create the way for them to come to the father.

The way to prepare the way, John explained was through repentance or changing of the way one saw things as well as the actions that would follow. John therefore brought about a change in the world view of the people. he baptized them i water but spoke of the one who would come after him who would baptize with the Holy Ghost and fire.

John brought a new perspective and renewed the hope in people of a coming messiah. As such by the time Jesus began his ministry, the idea of the coming messiah was quite common and Jesus's role therefore was to teach and demonstrate the role of the messiah and fulfill the calling.

I can think of a few reasons but there are probably much more.  

First, as Jesus was not ordained by the existing authorities and seemed on the surface to take things in a different direction from the Old Testament, a forerunner which was prophesied to herald his coming, not only fulfills prophecies of Elijah's return but creates a smooth transition from the Old to the New Covenant where the prophets directly lead up to the entire end of all their prophecies in Christ. What I mean is John was like a typical prophet denouncing sin and calling for repentance with a kind of rugged Old Testament asceticism and harshness, somewhat different from the meek and mild Jesus that pronounced peace and grace.  When the Jews questioned Jesus on how he derived his authority to preach and to heal (since he was not recognized by the 'authorities' of tradition) he asked them what they thought of John the Baptists (Mark 11:29). The question was intending to show them that they were so cowardly (not admitting that they did not believe in John the Baptists among the crowd) that they were not worth responding to, but still the connection to the Baptists is made regarding recognition of an 'authority', besides the direct testimony of God the Father of course.

Second, that a great prophet such as John was, in his humbly recognizing Jesus as so much greater, properly introduced the Messiah. (Matthew 3:11)

Third, his baptism of the Jews by John was a kind also used to convert Gentiles to Judaism, so like Elijah he was making a great call to repentance communicating to everyone, even those who thought they were holy, must prepare for full repentance and be prepared to receive the Messiah.  This mission was like Elijah. 

Fourth, The idea that Elijah would come just before the Messiah (literally Elijah, not someone like him) was completely expected by rabbinic tradition, so the fulfilled prophecy was no small matter, even though, as many of the other fulfilled prophecies, we're not fulfilled in ways expected, as a whole they became a strong testimony on Christ's authenticity.