Jesus was sinless and didn't need to be baptized by John as a repentance from sin. We know this because of the many places in scripture Jesus' sinlessness is confirmed.

However, Jesus did ask John to baptize him anyway, even though John was aware that Jesus wasn't a sinful candidate, in that John knew Jesus' identity and what His purpose on earth was.

John-'Behold the lamb of God who takes away the sin of the world.' John 1:29

Jesus may have gone the second mile in obedience to the Father, perhaps hearing the Father call the people to baptism through the prophet John, Jesus simply obeyed the Father as He always did, even though He had no sin to repent of.

Since elsewhere in the NT, the 'baptism of John' and the 'baptism of Christ' are treated as two different things by the disciples, it's important to see that Jesus' baptism here could have other meanings since it was not repentance from sin, meanings that may have to do with Jewish spiritual acts. Please see link below for clarification on water submersion as a Jewish spiritual rite.

http://www.jewsforjesus.org/publications/issues/v02-n10/baptism

"Though the only Biblical requirement for entrance into the covenant was circumcision, baptism became an added requisite. No one knows exactly when or by whom the requirements were changed to include baptism, but it was before the time of Jesus. We know this, because debates on the subject of proselyte baptism are recorded between rabbinic schools of Shammai and Hillel, both contemporaries of Jesus. Whereas the school of Shammai stressed circumcision as the point of transition, the Hillelites considered baptism most important because it portrayed spiritual cleansing and the beginning of a new life." from above link.

Jesus may have been comfirming Himself to the Father in holiness, and showing to all His commitment to the Father and His will, by receiving the water baptism.

He may have received baptism to show He believed in John's message, that it was from God, and showed His willingness to follow God and John in whatever way was asked.

I believe this water baptism of John was about more than for the repentance from sin, water baptism (see JewsforJesus link) was a sign of a proselyte following a prophet, and Jesus was submitting Himself to God through John Baptist's prophethood. There is a Jewish rite called the mikveh that means submersion in water for spiritual reasons that dates back to before the time of Christ. see wiki, http://en.wikipedia.org/wiki/Mikveh

This baptism that Christ received is not the baptism that the CC or other Christian churches practice when baptism is performed. The Christian church's baptism in water is an indication of the new birth into Christ Jesus and into His New Covenant, as well as for adults receiving this- as a repentance from sin.

John was a prophet of the Old Covenant and while he was calling the people back to obedience to God, and turning away from their sins, he was still practicing the Jewish faith and Jewish water immersion, not our Christian water baptism into the New Covenant with Christ.

The bottom line in Jesus receiving John's water baptism is that Jesus was saying "I obey God and follow Him and do all to accomplish that", Jesus was submitting Himself to all that was 'of' God.

Another point that is pertinent to the baptism of John Baptist being separate and different from the baptism into Christ, is that we find the disciples of Jesus finding those who were baptized by John, re-baptizing them in the name of Jesus, in the NT. This is an important pt to note when understanding what the baptism of John was.

The most prevalent answer to your question, by some would be original sin. but if we take a longer look at the passage in Mark, for instance:

Mark 1:7 and 8 And preached, saying, There cometh one mightier than I after me, the latchet of whose shoes I am not worthy to stoop down and unloose. 8 I indeed have baptized you with water: but he shall baptize you with the Holy Ghost.

Later on when Jesus came to John to be Baptized by him the following occurred:

Mark 1:9 through 11 And it came to pass in those days, that Jesus came from Nazareth of Galilee, and was baptized of John in Jordan. 10 And straightway coming up out of the water, he saw the heavens opened, and the Spirit like a dove descending upon him: 11 And there came a voice from heaven, saying, Thou art my beloved Son, in whom I am well pleased.

Matthew in the same scriptural passage has this in addition:

Matthew 3:15 And Jesus answering said unto him, Suffer it to be so now: for thus it becometh us to fulfil all righteousness. Then he suffered him.

If we take these together we must conclude that true baptism is Baptism with the Holy Ghost; or Holy Spirit. And now we need to examine what Jesus meant by 'thus it becometh us to fulfil all righteousness.'

Jesus came to fulfill the law and the Prophets:

Matthew 5:17 Think not that I am come to destroy the law, or the prophets: I am not come to destroy, but to fulfil.

and during this event the following prophesy was fulfilled:

Isaiah 42:1 through 4 Behold my servant, whom I uphold; mine elect, in whom my soul delighteth; I have put my spirit upon him: he shall bring forth judgment to the Gentiles. 2 He shall not cry, nor lift up, nor cause his voice to be heard in the street. 3 A bruised reed shall he not break, and the smoking flax shall he not quench: he shall bring forth judgment unto truth. 4 He shall not fail nor be discouraged, till he have set judgment in the earth: and the isles shall wait for his law.

It seems that the answer to why Jesus even though sinless was fulfilling Isaiah's prophesy. Otherwise he could not have fulfilled all prophesy.

This is my understanding from the Scriptures contained in the King James translation which is recognized as canonical by my Southern Baptist faith.

Hope this helps

As the Catholic Church understands the sacrament of baptism today, it has two purposes:

1. Initiation: Baptism makes a person a member of the Church.

   Baptism is birth into the new life in Christ. In accordance with the Lord’s will, it is necessary for salvation, as is the Church herself, which we enter by Baptism.

   (Catechism of the Catholic Church paragraph 1277)

2. Absolution:

   By Baptism all sins are forgiven, original sin and all personal sins, as well as all punishment for sin. In those who have been reborn nothing remains that would impede their entry into the Kingdom of God, neither Adam’s sin, nor personal sin, nor the consequences of sin, the gravest of which is separation from God.

   (Catechism, paragraph 1263)

Of course, neither of these could have applied to Jesus Himself. As the Catechism states, Jesus wanted first of all to identify with the sinners he had come to save:

Our Lord voluntarily submitted himself to the baptism of St. John, intended for sinners, in order to "fulfill all righteousness." [Matt. 3:15]

(Catechism, paragraph 1224)

The explanatory note on Matthew 3:14–15 in the New American Bible includes a discussion of this quoted text:

To fulfill all righteousness is to submit to the plan of God for the salvation of the human race. This involves Jesus’ identification with sinners; hence the propriety of his accepting John’s baptism.

Similarly, the NAB's note on Mark 1:8–9 (the same story) states:

Through the life-giving baptism with the holy Spirit (Mk 1:8), Jesus will create a new people of God. But first he identifies himself with the people of Israel in submitting to John’s baptism of repentance and in bearing on their behalf the burden of God’s decisive judgment.

Jesus begins his ministry by emptying himself, by kenosis: "he emptied himself ... he humbled himself" (Philippians 2:7–8). Though not needing to be forgiven, he acted as a human in need of forgiveness; thus he showed more fully the seriousness with which he took his mission of redemption.

What was John's baptism?

An academic paper from Colin Brown offers an answer by surveying the historical context of John's baptism, and the (scant) details we're provided about John himself. I'll attempt to summarize his key points:

• The traditional picture of John standing in a waist-deep river, trickling water over people's heads is 'a scene of pious fiction'.
• The Jordan River was remote, thus not ideal for people to travel to during the warmer months. It was also 'impossible for mass baptisms'.
• The Jewish mikveh was for ritual cleansing, and didn't necessarily involve 'washing' away some sin. In contrast, John's baptism was specifically a call for repentance. (Not to mention the Jordan River was shallow and dirty, an inappropriate place for a cleansing ritual.)
• Josephus' description of John says he taught the Jews to live 'righteous lives', and that they were to be 'unite[d] by baptism'.

With these points in mind, Brown turns to a specific detail about John himself: he patterned his life and mission after Elijah, and there is one episode from Elijah's career that involved the Jordan River.

In particular, the crossing and recrossing of the Jordan in the consecration and empowerment of Elisha as Elijah's successor appears to contain echoes of the earlier Joshua story. In both cases the waters parted and the crossing was effected on dry ground. Although John was no miracle worker, the story may be of some significance in view of the Baptist's reputation as an Elijah redivivus.²

In this line of thought: Israel crossed the Jordan in order to enter the promised land that God had promised in his covenant with the nation. Elijah directed Elisha to cross the Jordan as a reenactment, as a sort of re-dedication to Israel's covenant with God; a clean slate in God's relationship to the nation.

John, patterning himself after Elijah, chose the Jordan River to carry out his own sort of re-dedication; those who repented and were baptized in the Jordan River, the original entry point into the promised land, were uniting as a renewed Israel in the face of John's message of 'the coming wrath'.³

This explanation may help to explain why John proclaimed a baptism of repentance for the forgiveness of sins. What he proclaimed amounted to a call to become a morally renewed Israel.⁴

Brown notes that John's symbolic use of the Jordan is not without precedent in this era. Josephus describes would-be revolutionary Theudas the Galilean as leading his people to the Jordan River, where he claimed he would be able to part the waters, à la Joshua or Elijah.

Jesus' baptism by John

In this view, Jesus being baptized was not to 'wash' away his sins. Because the baptism was altogether a symbolic enactment of one's commitment to a repentant, righteous, reconstituted Israel in the face of 'coming wrath'... Jesus insisted on his own baptism to symbolize his own commitment to that mission. It was a participation not out of personal guilt, but out of duty to the nation of Israel as a whole.

¹ Colin Brown, 'What Was John the Baptist Doing?', Bulletin for Biblical Research 7 (1997), p.37-50.

² Ibid., p.45.

³ I would further suggest this focus on a 'renewed Israel' helps makes sense of John's statement in Matthew 3.9; God's desire is for a purified Israel to fulfill his promises to Abraham.

⁴ Ibid., p.46.

Jesus' baptism was not a confession of guilt. He fulfilled the rite of baptism because He identified Himself as one of us, taking the steps we are to take. His life of perfect submission here on earth is an example to us.

Matthew 3 (NKJV)

14 And John tried to prevent Him, saying, “I need to be baptized by You, and are You coming to me?”

15 But Jesus answered and said to him, “Permit it to be so now, for thus it is fitting for us to fulfill all righteousness.” Then he allowed Him.