Just who were these Jewish believers? What did they believe and why?
We will never (this side of the World to Come) know much about the Ebionites because they left us no writings and those who wrote about them were quite biased against them. We can only piece together a little about them. Skarsaune does a good job of getting down to what we can know.
In considering our sources on the Ebionites, all writers from the time of the church fathers, one major branch of evidence is the Irenaeus-Tertullian-Hippolytus-Pseudo-Tertullian branch. Skarsaune considers these writers as one branch since they all seem to rely more on Irenaeus’s initial description of the Ebionites than on any actual experiences they had themselves. In other words, Skarsaune makes a good case that Irenaeus created a stereotype and later writers simply added to it.
The following are the major passages about the Ebionites, which I will follow with a few comments:
Irenaeus, Against Heresies 1.26.2,