Since the early Church and ancient Israel, baptism symbolized repentance. But repentance entails a sinner. Since Jesus was sinless, the question naturally comes up - why was he baptized?
In Matthew 3:15 Jesus answers, "Let it be so now, for thus it is fitting for us to fulfill all righteousness." (ESV). Aside from this very confusing response which can be interpreted in a million ways, the usual criticism is that the Gospels are trying to cover up that Jesus never pretended to be a sinless Messiah (at least not at first), and that he was originally a disciple of John the Baptist.
Thus goes the argument from non-conservatives: the Gospels and their Christian traditions mythologized Jesus to the point where he was a miracle-worker Savior of the world. But they couldn't/wouldn't hide the fact that he was baptized by John (all four mention it), and only one of them bothers to explain why with literally one cryptic sentence. Clearly no one was embarrassed by this and everyone understood why. This also shows the early Christian tradition was reliable and could not be made up; at least not on the large scale non-conservative scholars maintain it was.
Significance of the Sacrament and Jesus' Baptism
Oscar Cullmann, who is no biblical conservative, wrote a very interesting examination of baptism and its role in New Testament theology. He explains how Jesus' baptism had a very deep significance both for his purpose and in connection to the Old Testament:
At the moment of his Baptism he receives the commission to undertake the role of the suffering Servant of God, who takes on himself the sins of his people. Other Jews came to Jordan to be baptised by John for their own sins. Jesus, on the contrary, at the very moment when he is baptised like other people hears a voice which fundamentally declares: Thou art baptised not for thine own sins but for those of the whole people. For thou art he of whom Isaiah prophesied, that he must suffer representatively for the sins of the people. This means that Jesus is baptised in view of his death, which effects forgiveness of sins for all men. For this reason Jesus must unite himself in solidarity with his whole people, and go down himself to Jordan, that 'all righteousness might be fulfilled.'
In this way, Jesus' answer to the Baptist...acquires a precise meaning. The Baptism of Jesus is related to dikaiosune [righteousness], not only his own but also that of the whole people. The word pasan [all] is probably to be underlined here. Jesus' reply, which exegetes have always found difficult to explain, acquires a concrete meaning: Jesus will effect a general forgiveness. Luke (like Mark) does not use this word, but he emphasizes in his own way the same fact at 3. 21: 'Now when all the people were baptised..., Jesus also was baptised.' [Cullmann, Oscar. Studies in Biblical Theology, No.1 (1950), p.18]
What Cullmann basically says is that Jesus' baptism inaugurated his mission, one as the [suffering] Servant of God - and the Bible agrees: Luke 3:23 immediately after the baptism episode says "Jesus, when he began his ministry, was about thirty years of age..."; Mark and John simply open with this episode without even an introduction like Luke or Matthew.
Josephus himself says that John's baptism was for the symbol of a pure heart and not that it actually cleansed from sin. Luke 3:3 agrees with this view if the "forgiveness of sins" applies to the repentance of the individual and not John's baptism, as I believe the verse should be read (cf. the exclusivity of only God and the Messiah to forgive sins directly: Mark 2:7-10). Matt. 3:6, 11a may seem to contradict this, but there is nothing that necessitates v.6 to mean that John was forgiving the sins versus the repentance of the confession of sins. And v.11b shows that the repentance was probably not a direct forgiveness of sins from John, or why differentiate his baptism from the new heart of the Spirit? It's possible that this is only symbolic since John is outraged at the corrupt Pharisees coming for the baptism which he presumably gives (v.11), but that's not conclusive, and he could've been speaking to everyone at that point. Finally, Jesus considers John a true prophet whose authority was from God (Matt. 21:23-27), but this doesn't mean that John forgave sins.
The symbol of the servant who is an example to others was a powerful exhortation for upright life in the early Church (Hebrews 2:14-18; Philippians 2:5-8). The baptism in that light, as Cullmann says, makes not only perfect sense, but is basically what one would expect (Rom. 8:29). Imagine a teacher who tells his elementary school students not to eat in class because he knows they'd make a mess, but is then seen eating in the classroom by them - it'd be a bad example for kids who wouldn't understand.
This view, supported by John's Gospel as Cullmann points, is connected to Jesus' use of the word "baptism" in connection with his death and resurrection (Mark 10:38; Luke 12:50). To this the meaning of the Christian's baptism is intimately connected with being born again (John 3:3) as a new person in Jesus' death (Rom. 6:3-4).
There are many more points and deeper connections and levels of significance as the author writes, but this best summarizes his idea:
It is clear in view of the voice from heaven why Jesus must conduct himself like other people. He is distinguished from the mass of other baptised people, who are baptised for their own sins, as the One called to the office of the Servant of God who suffers for all others." [ibid., pp.18-19]
Jesus' baptism accomplished the following:
- Inaugurated his mission as the Servant of God: both as a symbol and in front of others (John 1:29-34)
- Symbolized his taking of mankind's sins as the voice echoes Isaiah 42:1 (cf. Isaiah 53)
- Set an example for his followers via a meaningful connection to his purpose and temporal destination (death and resurrection)
- It is for this reason that Matthew 3:15 rightfully says that this was to fulfill all righteousness.