Missional work in Ephesus (ruins to the right) involves plenty of unplanned-for work, namely ushering some disciples of John the Baptist into the fullness of the Pentecost era.

19:1 While Apollos was in Corinth, Paul went through the inland regions and came to Ephesus. He found some disciples there 19:2 and said to them, “Did you receive the Holy Spirit when you believed?” They replied, “No, we have not even heard that there is a Holy Spirit.” 19:3 So Paul said, “Into what then were you baptized?” “Into John’s baptism,” they replied.19:4 Paul said, “John baptized with a baptism of repentance, telling the people to believe in the one who was to come after him, that is, in Jesus.” 19:5 When they heard this, they were baptized in the name of the Lord Jesus, 19:6 and when Paul placed his hands on them, the Holy Spirit came upon them, and they began to speak in tongues and to prophesy. 19:7 (Now there were about twelve men in all.)

There is a salvific difference, or least a life-difference, between the baptism of John (repentance and into the future Messianic work) and the baptism of the Spirit (repentance, death and resurrection of Christ, and Spirit endowment). They needed a baptism into the Lord Jesus, and when they were, they received the powerful Spirit — and spoke in tongues and prophesied, and this demonstrated the presence of God’s Spirit.