Jesus came to fulfill all His Father’s plans. This included not only fulfilling the Law of Moses but every avenue of obedience to God. Jesus said in His own words that He desired baptism in order to fulfill all righteousness. Exactly what “fulfilling all righteousness” really means has been discussed by scholars for a long time. Allow me to give you a few thoughts from some of these scholars.
Jesus needed to be washed and anointed for ministry.
Dr. Adam Clarke says: “There was a kind of baptism among the Jews, viz., that of the priests at their consecration (Leviticus 8: 6). Now, as Christ had submitted to circumcision (as a child), the initiating ordinance of the Mosaic dispensation, it was necessary He should submit to the initiating ordinance of the Christian dispensation, instituted by the same authority (the Lord God). But it was necessary on another account.
Our Lord represented the High Priest, and was to be the High Priest over the house of God; now, as the High Priest was initiated into his office by washing and anointing, so must Christ be; hence. He was baptized, and anointed by the Holy Ghost. Thus He fulfilled the righteous ordinance of His initiation into the office of the High Priest, and was prepared to make an atonement for the sins of the whole of mankind.
Jesus needed to be made eligible to become the perfect Lamb offering.
Dr. Donald Grey Barnhouse comments:
The Lord Jesus allowed himself to be baptized in fulfillment of the type of the ceremonial law, as we see in the first chapter of Leviticus. The pieces of the body of the lamb were washed with pure water before they were placed on the altar to be consumed as the burnt offering.
And when John identified the Lord Jesus as being spotless without, the voice came from Heaven, saying, “This is my beloved Son, in whom I am well pleased” (Matthew 3: 17). Thus did God pronounce His Son to be spotless within. By permitting himself to be baptized, the Lord Jesus announced to Earth and Heaven that He was the spotless Son of God, and eligible to die.
Jesus had to become identified with His people in all things.
Frederick L. Godet makes this observation:
The term Lamb of God is so original that, if it is historical, it must have its ground in some particular impression which the Baptist had received at the time of his previous meeting with Jesus. And indeed, we must remember that when an Israelite came to have himself baptized by John, he began by making confession of his sins (Matthew 3: 6; Mark 1: 5).
Jesus could not have dispensed with this preparatory act without arrogating to himself from the first an exceptional position, and nothing was farther from his thought than this: He wished to “fulfill all righteousness” (Matthew 3: 15). What, then, could His confession be? Undoubtedly a collective confession, analogous to that of Daniel (Daniel 9), or that of Nehemiah (Nehemiah 1), a representation of the sin of Israel and of the world, as it could be traced by the pure being, who was in communion with the perfectly holy God, and at the same time the tenderly loving being, who, instead of judging His brethren, consecrated himself to the work of saving them.