Jesus might well have been up there in front standing with John and calling on sinners to repent. Instead he was down there with the sinners, affirming his solidarity with them, making himself one with them in the process of the salvation that he would in due course accomplish. If there is a reference to Isaiah 53, it is relevant to note that in that chapter we read: he "was numbered with the transgressors" (Isa. 53:12). There may also be something of the Israel typology here. Jesus himself had no need of repentance, but Israel certainly did; in submitting to John's baptism Jesus is pointing to the people's need. Matthew pictures Jesus as dedicating himself to the task of making sinners righteous, an appropriate beginning of his public ministryMatthew Commentary
It was not customary, however, among them to baptize those who were converted to the Jewish religion until after the Babylonian captivity. At the time of John, and for some time previous, they had been accustomed to administer a rite of baptism, or washing, to those who became proselytes to their religion; that is, to those who were converted from being Gentiles. This was done to signify that they renounced the errors and worship of the pagans, and as significant of their becoming pure by embracing a new religion.https://www.studylight.org/commentaries/bnb/matthew-3.html