John the Baptist, the Herald of the King, is not introduced. See Luke 1:15-17 for the angelic announcement of his birth and mission. He is predicted in the Old Testament. Isaiah x1:3-5, Mal. iii:1. He appeared like Elijah the Prophet (2 Kings i:8). But He was not Elijah. See also Matthew xvii:12. And before the King comes the second time there will be once more a forerunner. Mal. iv: 5-6 will then be fulfilled. John knew his mission (John i:23). His testimony as reported by Matthew concerns the nation. In the Gospel of John we find the record of another testimony given by the forerunner. He knew the King also as the Lamb of God.
 

He calls the nation to repentance, because the Kingdom of heaven is at hand. The phrase "Kingdom of heaven" (literally "of the heavens") occurs here for the first time. It does not mean the offer of salvation, nor does it mean the church, nor the social betterment of the people, but it signifies the Messianic Kingdom as promised by the Prophets of God, a Kingdom which is to be set up on earth and over which the Son of David is to be King. This the forerunner announced. This Kingdom the Lord Jesus and His disciples preached, till it became evident that Israel would not have this Kingdom. Then the preaching ceased.
In verses 11 and 12 there is a blending together of the first and second coming of Christ. As a result of the first coming of Christ the baptism with the Holy Spirit took place. The fire baptism refers to judgment. The twelfth verse describes the fire baptism of judgment when the King comes again.

The baptism of John has nothing to do with Christian baptism. It was baptism unto repentance only. By being baptized in Jordan (the type of death) they confessed that they had deserved death.
Then the King entered upon His public ministry. He too entered the waters of Jordan and was baptized; not that He needed it, but to signify He came to be the substitute of sinners and to take the sinners' place in death. In the baptismal scene we have His whole blessed work foreshadowed. He is the holy One, who needed no baptism for He had no sin. His death is foreshadowed when He went into Jordan; His resurrection, when He came out of the water; His ascension, when Heaven was opened unto Him. The gift of the Holy Spirit is seen next and this is followed by the declaration of Sonship. Into this the believer enters. We are dead and risen with Him; Heaven too is opened unto us and we have received the Spirit of Sonship.