Even the so-called Judaeo-Christian Gnostics (Cerinthus), the Ebionite (Essenian) sect of the PseudoClementine writings (the Elkesaites), take up an inconsistent attitude towards Jewish antiquity and the Old Testament.
The conception of a resurrection of the body, of a further existence for the body after death, was unattainable by almost all of the Gnostics, with the possible exception of a few Gnostic sects dominated by Judaeo-Christian tendencies.
Thus we are forced to assume the use of a certain amount of early Judaeo-Christian material, akin to that implied also in the special parts of the Third Gospel.
This goes to the root of their difficulty, ambiguity as to the relation of the old and the new elements in Judaeo-Christian piety, so that there was constant danger of the old overshadowing the new, since national Judaism remained hostile.