Luke intended this paragraph to be read along with the previous unit, the introduction of Apollos as a disciple of John. Just as Luke contrasted Barnabas with Ananias in 4:36-28 and 5:1-2, Apollos and the other disciples of John stand in contrast One disciple heard John and accept Jesus as the Messiah (although not fully understanding the implications of the resurrection, most likely with respect for Gentile salvation), the other disciples heard John but were ignorant of Jesus and the Holy Spirit.
The dozen disciples of John indicate that even 20 years after John’s death there was a movement amount the Jews that held John to be a prophet and in some way kept his teachings alive. Perhaps the gospel of John gives us a similar hint, especially if it can be show that John wrote from Ephesus near the end of the first century.
These disciples cannot be considered Christians at this point since they had not yet received the Holy Spirit. While Luke only uses “disciple” for believers in every other case in Acts, his use of μαθητής here is without a definite article, the such example in Acts. At the very least these are unusual Christians, perhaps “fringe” Christians, similar to the “unusual, fringes of Judaism described in the first half of the book. Paul’s question – did you receive the Holy Spirit – is equivalent to asked, “are you believers?” Not only have these disciples not received the Holy Spirit, they do not even know that there is a Holy Spirit!
Paul asked them “into whom” or “into what” they were baptized. The NIV obscures this a bit, interpreting the question as “who baptized you,” rather than “what was the medium in which you were baptized.” Witherington comments that the image of being immersed into the Holy Spirit was common in the early church, see Rom 6:3, 1 Cor 1:13, 15, 10:2, 12:13, Gal 3:27). His point is that the “whom” of this verse cannot refer to water; he sees the baptism of the Holy Spirit as entry into saving faith, while baptism in water is entry into the Christian community (Acts, 571).
Since they had been baptized “in John’s baptism,” Paul explains that John’s baptism was not enough, it was a “baptism of repentance,” which looked forward to the ministry of Jesus. One could not be saved at this point in history only by accepting the message of John, it is only through faith in Jesus that one can be saved (as Acts has made abundantly clear prior to this point in the book!)
As has happened at several points in the book of Acts already, there is a manifestation of the Holy Spirit (tongues and prophesy) after Paul lays hands on these disciples. There is no consistent “order of events” in Acts, sometimes the Spirit comes prior to baptism (10:44-48, Cornelius) and other times baptism is prior (19:1-7), and in the case of Apollos, there is no mention of a re-baptism or of the coming of the Spirit. Perhaps this is because he properly understood the message of John as pointing forward to Jesus, but that is not clear.
In fact, this is the only case of re-baptism in the New Testament, even the twelve were not re-baptized into the name of Jesus, they only had experienced the baptism of John (although one wonders about Matthew, since he was called to be an Apostle after John’s ministry.) The point of this brief narrative is to show that it is possible to have a limited knowledge of Jesus which is not enough to be saved – theologically there was nothing wrong with these disciples except that they did not quite believe enough. They did not believe something that was wrong, but they did not take their belief to the full extent needed for salvation.
Here is another problem for Applying Acts – what do we make of these disciples? Are these disciples “partial believers” who have participated in a ritual (John’s Baptism) but did not believe enough to be actually Christians? What is it that “saved” these disciples? In any case, it is the reception of the Holy Spirit which demonstrates they are in fact now Christians.