That's not the whole verse. It's "being not baptized of him [John the Baptist]". The rejected his message of repentance, which the baptism represented. Just as now, Baptism had no saving power in itself.
Baptism as a work of God is "by one spirit into one body" (1 Cor. 12:13), meaning that we are "immersed" into the body of Christ. This is the baptism that "doth now save" (1 Pet.3:21). The water ceremony was to accompany it; but over time, as the Church developed into a series of conflicting organizations, it became no longer feasible to baptize someone immediately on conversion. You can see this, (and its unofficial replacement, the altar call), discussed at http://members.aol.com/etb700/baptism.html.
As for another of those essentials; even though Oneness (modalism) on the surface accepts the deity of Christ, still, I notice that when you press them on how Christ can pray to the Father, sit at His right hand, and whether the Father died on the Cross (patripassianism); they will often start to separate the two natures of Christ into practically two separate entities: a divine Christ that unites to a purely human Jesus. This then does compromise the true deity of Christ, and becomes nearly identical to progressive monarchianism (the theology of the Way Int. or Christadelphians)
