Publishers often don't like it. It's always a first draft and thus not polished. It exposes me to unnecessary criticism from people I might otherwise be on good terms with (and I'm not talking of a single unified group but people who switch back and forth from fan to opponent depending on the issue). For these reasons it is unfortunate that I write with the greatest motivation and style when there is at least a possibility that someone is listening and enjoying. So I'm going to try to jump start some scholarly writing today by writing a few hundred words here...
... The form of Judaism to which they [Gentiles] were converting would have been the Christian Judaism of the previous chapter. These were Jews who did not see their faith as an alternative to Israel's faith but as its truest understanding and culmination. Arguably, Christian faith in Jesus as Messiah initially assigned a name to the messianic expectation of other Jewish groups. These were groups looking for God to restore the kingdom of Israel by way of someone from the Davidic line.  In earliest Christianity, this faith almost immediately transformed into something much more extensive in scope. Nevertheless, as we will argue in a subsequent chapter, it did not cross any obvious line in the first century that would clearly have demarcated it as a separate religion from its parent Judaism. 
The ritual of baptism in itself was not uniquely Christian. The most unique feature of the baptism of John the Baptist was its "one time" nature.  That is to say, ritual washings were a normal part of temple purity, indicated by the numerous miqvaot or cleansing pools throughout Israel.  The site at Qumran had such a pool at both of its entrances. Perhaps you descended unclean down into the water on one side and then ascended clean on the other, now purified to enter the Qumran community.  What distinguished the baptism of John was the fact that it arguably was preparing for a unique event in history, the arrival of the restored kingdom of Israel on earth.  It was thus conceptualized to be a one time event before the arrival of the promised king.
The origins of early Christian thinking about the Spirit perhaps involved the convergence of several trajectories. In this regard, Joel 2:28-32 surely played an important role, and it was probably connected with other important passages for early Christian understanding such as the new covenant imagery of Jeremiah 31 and the association of Jesus with passages in Isaiah. The Dead Sea Scrolls indicate that imagery of God's holy spirit was already in use within Israel,  and the miracles of the early church no doubt provided ample events with which to link God's Spirit.  By the time we reach the book of Acts, baptism associated with the Holy Spirit came to distinguish baptism in Jesus' name from the baptisms performed by John the Baptist (cf. Acts 19:1-7).
All of these distinguishing elements within Judaism were intra-Jewish distinctions rather than distinctions that would have separated Christian Jews from Judaism "proper."  In relation to Gentiles, the earliest Christians debated what a Gentile would need to do in order to be fully "in" the people of God...
 It is not at all clear that all Jewish groups of the time had this expectation (see James H. Charlesworth, The Messiah: Developments in Earliest Judaism and Christianity [Minneapolis: Augsburg Fortress, 2009]). The best known text in this regard is Psalms of Solomon 17. The provenance of Psalms of Solomon is not agreed, although some have suggested it could be Essene (***). The Dead Sea Scrolls also have a few messianic texts (***; see John J. Collins, The Scepter and the Star.
 See chapter 5. As we will argue, this interpretation is true in part because the Judaism of the time did not have entirely clear boundary lines in the first place in relation to what it meant to believe in "one God."
 *** James VanderKam...
 Whether one believes that supernatural miracles can occur or not, it seems beyond question that the earliest church could identity any number of events that it considered to be miracles, not only in the ministry of Jesus but also in the early church. See ***.
 We remember from the first chapter that Judaism at the time of Christ was diverse enough that many prefer to speak in terms of Judaisms rather than Judaism at the time as some monolithic entity. See pp. **.