The logic of Acts 19:4, rather, seems
to be that Paul is informing the Ephesians of three facts:
(1) John’s baptism, which they have
experienced, is not self-referential but only a baptism of repentance preparing
people for something else.
(2) That “something else” is a person in whom John wanted his baptizands to
believe.
(3) The name of that person is Jesus.
The words τοῦτ’ ἔστιν εἰς τὸν Ἰησοῦν
(“that is, into Jesus”), in this context, imply the unveiling of a previously
unknown name; it is upon hearing this name, and into it, that the Ephesians are
immediately baptized. If Luke calls these baptizands “believers” and
“disciples,” terminology that he elsewhere reserves for Christians, this is
because he has refashioned the image of the Ephesian adherents to fit his own
Christian theology, in which followers of the Baptist of course believe
in Jesus too. Although this superimposition introduces a narrative
inconsistency into
Acts, that is a small price for Luke
to pay for being able to assert that followers of John are naturally followers
of Jesus as well—and that, if any are not, they will quickly become so on
hearing the good news. (Joel Marcus, “Appendix 6: Knut Backhaus’s Interpretation
of Acts 19:1-7,” in John the Baptist in History and Theology [Studies on
Personalities of the New Testament; Columbia, S.C.: University of South
Carolina Press, 2018], 137-38)
Commenting
on the immediate baptism of those at Ephesus:
For Backhaus, Die
“Jungerkreise” des Taufers Johannes, 207, this
immediate baptism is evidence that the Ephesian “disciples” have a previous
history of adherence to Jesus, since the proclamation about him in 19:4 is so
short, in contrast to missionary proclamations elsewhere in Acts (2:14–36,
3:12–26, 4:8–12, 10:34–43, 13:16–41). But the Phillipian jailer is converted
after hearing only the exhortation, “Believe in the Lord Jesus, and you will be
saved, you and your household” (Acts 16:31), and the Ethiopian eunuch is
converted in a similarly quick manner (8:35–38). Such conversions may not be
psychologically plausible, but they fit Luke’s narrative style. (Ibid., 227 n.
4)