Matthew 3:11 says - "I indeed baptize you with water unto repentance, but He who is coming after me is mightier than I, whose sandals I am not worthy to carry. He will baptize you with the Holy Spirit and fire." John affirmed that his baptism was "unto repentance" ; that is, he baptized them that they would do the works of righteousness that would show their repentance (cf. Luke 3:11-14).
John freely admitted that he was not the Christ. Rather, the Messiah would come after him. He goes on to describe just how insignificant he is in comparison to the Messiah who was to come. John proclaimed that he was unworthy to carry Christ's sandals or even bend down and unloose His sandal strap (Luke 3:16)! This is an expression of intense humility since untying or carrying away the shoes of the master or his guest was the work of the lowest slave of a household. John is essentially saying that the people shouldn't consider him to be the Christ for he doesn't even consider himself worthy enough to be a servant of the Messiah!
John then states that Christ "will baptize you with the Holy Spirit and fire." Many interpret this as a reference to that which happened on Pentecost in Acts 2. While it is true that in that context the apostles did experience the baptism of the Holy Spirit, I do not believe they were baptized in fire! Yes, there were divided tongues "as of fire" resting upon them (Acts 2:3), but that doesn't mean they were immersed with fire! We have seen in Matthew 3 that John the baptizer has been describing two types of people, faithful and unfaithful, and he is now discussing two separate baptisms. The casting of the unfruitful trees into the fire represents the punishment of the wicked (verse 10) and the burning of the chaff with fire represents the same in verse 12. Thus, according to the force of the context, the baptism of fire here in verse 11 would logically have the same reference. The baptism of fire is not an experience one should desire. The wicked will experience such a baptism when they are "cast into the lake of fire" (Rev. 20:15).
Matthew 3:12 reads - "His winnowing fan is in His hand, and He will thoroughly clean out his threshing floor, and gather His wheat into the barn; but He will burn up the chaff with unquenchable fire." The figure used here was taken from the custom of threshing grain by treading it out with oxen or by drawing a threshing tool over the grain. As a result, the grain and chaff were mingled, and in this condition both were thrown up against the wind with a shovel. This resulted in the chaff being blown away while the grain, which was heavier, fell into a heap. In this way, chaff and grain were separated. Afterward, the chaff was burned up and the wheat was gathered into the barn for storage. John's words here represent the Messiah as separating the evil from the good (Matt. 25:32,33). The worthy are received into His kingdom and given a rich reward, while the unworthy are destroyed. There is a sharp contrast between the wheat and the chaff as well as the destiny of the two classes. The fire that burns the wicked is "unquenchable" which means it is never extinguished; the doom it describes is eternal (Matt. 25:46).
As we conclude this series on John the baptizer, I hope it is plain to see that John was quite a preacher. He delivered God's word powerfully and uncompromisingly to the people of his generation. He humbly fulfilled the work that God intended for him to accomplish, always seeking to direct attention to the Lord, not himself. What a wonderful servant John was!