Paul's Ministry in Ephesus among The Disciples of John the Baptiser (19:1-7).
Meanwhile Paul, having encouraged the churches in Phrygia-Galatia arrived via the mountain regions in Ephesus. There he came across a group of believers, possibly in the synagogue, who seemingly honoured Jesus and yet whose lives were lacking the glow of the Spirit. Whether these were original disciples of John, or merely those who had received Apollos' teaching before he himself had had his eyes opened, we do not know. Had they been Apollos' converts, however, we might have expected Luke to say so.
But spread around the Jewish world were large numbers of disciples of John the Baptiser. They had responded to his teaching on various visits to Jerusalem and their hearts would be waiting for the full truth about Jesus. Yet it was important for all, and especially Jews, to recognise that they were not Christians (although hopefully Christians-in-waiting), nor were they an alternative to Christianity. Thus in this incident it is made quite clear that if these disciples of John are to be true Christians they must come to believe fully in Jesus Christ, and must be baptised and given the Holy Spirit, and thus become one with the Christian church. This fact is now emphasised.
But this incident is important in another respect. Paul had not been present at Pentecost. He had only heard of what had happened. But now he was to see something of it for himself. It would be like a new Pentecost. The Holy Spirit would be poured out and men would speak with other tongues. As far as Acts is concerned this is Paul's first experience of it. It would be a boost in preparation for what was to come.