15 Now the people were filled with expectation, and all were asking in their hearts whether John might be the Messiah. 16 John answered them all, saying, “I am baptizing you with water, but one mightier than I is coming. I am not worthy to loosen the thongs of his sandals. He will baptize you with the holy Spirit and fire……. 21 After all the people had been baptized and Jesus also had been baptized and was praying, heaven was opened 22 and the holy Spirit descended upon him in bodily form like a dove. And a voice came from heaven, “You are my beloved Son; with you I am well pleased.”
John contrasts his baptism with that of Jesus. The point is not that one baptism is with water, the other in the Holy Spirit and fire (the early church also baptized in water from the beginning), but that John’s baptism is only in water, that is, a ritual sign expressing outwardly what the person must express inwardly. The baptism of Jesus will be definitive: it will be an act of God bringing salvation (Holy Spirit) and judgment (fire). The image of fire is expanded by reference to the process of separating wheat from chaff. A “winnowing fan” or shovel tosses the mixture into the air; the heavier kernels of wheat fall to the floor, while the chaff blows away for later burning (Isa 21:10).
Culpepper (“Luke”, New Interpreter’s Bible, 85-6) offers the following:
“What is the relationship between Spirit and fire in this saying? The following interpretations have been advanced: (1) fire describes the inflaming purifying work of the Spirit; (2) the repentant will receive the Spirit, while the unrepentant will experience the judgment of fire; (3) since the Greek term for “Spirit” can also mean “wind,” the meaning is that Jesus’ baptism will bring the judgment in a mighty wind and fire; (4) as might be implicit in the first option, “Spirit” or “wind” and “fire” reflect the Christian interpretation of the Pentecost experience; or (5) John saw in Spirit and fire the means of eschatological purification: the refiner’s fire for the repentant and destruction for the unrepentant. The last combines elements of (2) and (3) and fits both the historical context of John’s preaching and the literary context in which the saying about winnowing follows. Luke, of course, may have seen the fulfillment of this saying at Pentecost in ways John could not have imagined.”
In v.18 we are told that John preached “good news.” This is part of the Lucan transition to move from the ministry of John to that of Jesus. We can assume John preached about the soon-to-come arrival of the Messiah. Craddock (Luke, Interpretation Commentaries, 49) offers this wonderful summary: “When repentance and forgiveness are available, judgment is good news (v. 18). The primary aim is to save the wheat, not to burn the chaff.” John offers hope and new life for the tax collectors, the soldiers, and all sinners. We all can be gathered by Jesus into his kingdom.
3:15 the people were filled with expectation: the word expectation (prosdokía) always carries a sense of either fear or hope
3:16 He will baptize you with the holy Spirit and fire: in contrast to John’s baptism with water, Jesus is said to baptize with the holy Spirit and with fire. From the point of view of the early Christian community, the Spirit and fire must have been understood in the light of the fire symbolism of the pouring out of the Spirit at Pentecost (Acts 2:1–4); but as part of John’s preaching, the Spirit and fire should be related to their purifying and refining characteristics (Ezekiel 36:25–27; Malachi 3:2–3).