As we read about in Matthew 3, John the Baptist breathed in an “atmosphere surcharged with the thought of the end.” In his mind his baptism was the final opportunity before “water” would be eschatologically outmoded by “the Holy Spirit and fire.” He thought that the time for repentance would reach its terminus with the appearance of the Christ—then water would be superseded by the Holy Spirit and fire, no longer for repentance but for final salvation and judgment.
Jesus, however, steps onto the scene and rather than enacting a redemptive-historical transition to his eschatological baptism, he comes to be baptized by John. But John protests. Now his protest was not for them to reverse roles as if Jesus was simply to administer John’s own baptism of water. Rather, John believes that it was now time for his baptism to be superseded by the eschatological baptism of Christ. In John’s eyes, the appearance of the Messiah alone was enough to transition redemptive-history into the eschatological era of the Messiah. His protest reveals he was ignorant of what must first be fulfilled in order for this to happen. This confusion over the timing and nature of Christ’s coming will persist with John and his disciples (9:9-13; 11:2-6).
In order to correct John’s redemptive-historical misunderstanding (or mistiming), Jesus responds, “Let it be so now, for thus it is fitting for us to fulfill all righteousness (Ἄφες ἄρτι, οὕτως γὰρ πρέπον ἐστὶνἡμῖν πληρῶσαι πᾶσαν δικαιοσύνην, 3:15). The first clause (“Let is be so now”) affirms that John was correct to expect a redemptive-historical transition, but it was not yet time—more than just the appearance of the Christ was necessary. It was thus fitting for Jesus to be baptized now (ἄρτι) because he and John had not yet fulfilled “all righteousness” (πᾶσαν δικαιοσύνην). If Jesus’ words are responding to this larger redemptive-historical timing issue, then it would seem natural to understand “all righteousness” here as including, but also going beyond his baptism to encompass all that he accomplishes in his life, death and resurrection. For it is only after these accomplishments that the transition John anticipated takes place and Christ commissions his disciples to baptize the nations in the name of the Father, Son, and Holy Spirit (28:19). Jesus, therefore, does not submit himself to John’s baptist as a mere example to be followed, but to propel redemptive-history forward in himself as the true Israel who repents not for his own sins, but for the sins of his people whom he came to save (1:21).
It is important to keep in mind that John does not administer a different baptism to Jesus; it is still a baptism with water for repentance on account of sin. Already the presence and problem of sin has been elucidated and deliverance from it has been tied to the mission of Jesus, the son of Abraham, the son of David (1:1). In Matt. 1:21 the people are understood not in the abstract, but specifically as those who belong to Jesus (“his people,” τὸν λαὸν αὐτοῦ) and who personally possess their own sins (“their sins,” τῶν ἁμαρτιῶν αὐτῶν). How is someone saved from their sin? Forgiveness (see 9:2, 5, 6; 12:31). And how is someone forgiven? By the poured out blood of Jesus Christ (see 26:28). Therefore, the death of Christ was a necessary redemptive-historical accomplishment for John’s preparatory ministry and the eschatological shift that he anticipated (16:21; 17:22-23; 20:17-19)—much more than the mere appearance of the Messiah was necessary.
In Matt. 3:6 we read of people confessing (ἐξομολογέω) their sins as they are baptized by John. In relation to Christ and his work, sin is forgiven by him and on account of him. In relation to people, sin is confessed. The confession (or repentance) cannot be isolated from its Christological basis, the death and resurrection of Jesus, that makes it effectual for salvation.
But we may be able to say more than this, for Jesus himself undergoes John’s baptism with water for repentance. As the true Israel (cf. 2:15), he makes a true confession of sins, not for his own sins, but vicariously for the sake of his people he came to save. In fulfilling all righteousness, “[Jesus] had no other calling than to comply with the demands that God had imposed on every Israelite. … [So Matthew] brings out Jesus’ solidarity with the human race and, indeed, with sinners.”
 Geerhardus Vos, Biblical Theology, 318.
 On the Holy Spirit and fire pertaining to salvation and judgment, respectively, see Herman Ridderbos, Matthew, 54. The same juxtaposition can be found in Ezek. 36:26-32; Joel 2:28-31; Zech. 12:9-10.
 Herman Ridderbos, Matthew, 57.
 It seems this is the same eschatological baptism expected by John, but now expanded to include the Father and the Son, possibly corresponding with the revelation of the Son by the Father and the Father by the Son (so 11:25-27).
 Herman Ridderbos, Matthew, 58-59.