I. Historical Sources for the Life of Jesus
A. Christian
These are: 1) The Canonical Gospels, (2) the Apocryphal Gospels, and (3) the rest of the New Testament (NT), notably Paul's letters.
(1-2) "Canonical" and "Apocryphal" represent a theological judgment made by the Church and not a historian's evaluation. The issue here is whether or not so-called "Apocryphal" Gospels like the Gospel of Thomas [Robert Miller, The Complete Gospels, 1992: 301-322] or the Gospel of Peter [ibid.391-401] are sources independent of the canonical four and so constitute evidence for the life of Jesus. The majority still say "no."
(3a). The chief source among the other writings in the NT are Paul's letters, esp. Rom., 1 Cor. and 1 Thess. They were written (ca. 50-57 CE) before any of the extant Gospels, but they are addressed to Christian communities and so presuppose that some version of the "Good News" has already been preached. There are some notable differences from the Gospels, chiefly that the events of Jesus life and his words and teachings are only rarely mentioned or cited. When they are, however, they attest to a carefully preserved oral tradition.
(3b) Finally, there are the beliefs and behavior of the earliest followers of Jesus as reflected in Paul and Acts. See, for example, the early "creeds" --expressed in a language and style quite different from the authors' own-- in Phil. 2 :6-11; Col. 1:15-20, and 1 Peter 3:18-22. Thus, shortly after Jesus' death, many of his followers "seem to have formulated a doctrine of atonement, were convinced that he had been raised from the dead in bodily form, associated Jesus with God, and believe d they found support for all these convictions in the OT."
These are: (1) The Biblical Apocrypha; (2) Dead Sea Scrolls; (3) Josephus; and (4) later rabbinic writings like the Mishna and Talmud.
(1) It is from the Biblical Apocrypha like Enoch and Baruch that we get our clearest idea of the apocalyptic and messianic ideas shared by Jesus' Jewish contemporaries and the authors of the Gospels.
(2) The Dead Sea Scrolls refers to a large cache of deliberately concealed documents discovered in 1947 near Qumran at the northwest corner of the Dead Sea. The writings, which date from the 2nd century BCE to the 1st CE, are distinctly sectarian --likely the "Essenes" described by Philo and Josephus-- and they describe a closed and highly organized community which is separatist, priestly, eschatological and messianic. Though there is little apparent resemblance to Jesus' own views in the sect's version of Judaism --the Essenes stand obviously closer to John the Baptist-- the Scrolls open another rich vein in the religious sensibilities of the first century Palestinian milieu from which Jesus emerged.