Both Jesus and John must adhere to justice, to all justice. Only these words convinced John to baptize Jesus, who considered himself superior to himself. Obviously, it is almost impossible to reconstruct the original scene of Jesus’ baptism, since Matthew’s gospel – like the other gospels – was elaborated by the Christian communities to which Matthew belonged, probably that of Antioch in Syria. In fact, the word justice is typical of Matthew’s vocabulary or of those who wrote his gospel. Justice for Matthew is the fulfillment of the plan of God enrolled in the Torah, i.e. the Law – the Pentateuch – the God’s will for all the Jews. Jesus was a Jew and certainly shared this way of thinking. However, every evangelist gives some special features to Jesus. Matthew’s Jesus is the one who acts according to a plan, a project enclosed in the Torah. But this plan overtakes it. In fact, there is also a superior justice through which you enter the kingdom of heaven (cf Mt 5:20).
But the will of God is not something abstract, but is fused with human will and therefore it consists of all the acts a human being puts in life. For John the Baptist, one of these acts was to baptize Jesus. That would be the sense of the phrase all righteousness, i.e. every act of which is composed the plan of God enclosed in the Torah and in the will go God.
John, perhaps, thought that his mission was that of becoming a burning preacher who patted the end of the world and punishment for sinners. But his only task was to baptize Jesus. This is the gesture that reveals his greatness, his invaluable contribution to the history of humanity. He could refuse to do so, but he would have missed his entire existence.
The fulfilling verb is, in this context, very important. God’s plan is like an empty form, or rather it is composed of only one part, the divine one. The human counterpart consists of many grains of sand. God needs us!