I thought it might be helpful to give one small example of how independent textual traditions can point back to what appears to be a common source in the historical Jesus. When I say these textual traditions are “independent”, I mean that scholars have concluded, based on differences in wording and grammar, that they did not simply copy from each other. Let’s look first of all at the Gospel of Thomas. The first layer, at least, of the Gospel of Thomas dates back to as early as 50 CE, according to Crossan, and internal evidence suggest the apostle James may have collected this first layer.
Here is Thomas 2 (Lambdin translation)
Jesus said, “Let him who seeks continue seeking until he finds. When he finds, he will become troubled. When he becomes troubled, he will be astonished, and he will rule over the All.”
Several other citations from Thomas have a similar theme:
(92) Jesus said, “Seek and you will find.”
(94) Jesus said, “He who seeks will find, and he who knocks will be let in.”
Several of the earliest Church fathers quote from a very early version of the gospel called “The Gospel of the Hebrews”. Unfortunately, no copy of this gospel survives, but based on analyzing the quotations, scholars believe this is an independent source written as early as 50–80 CE. The following fragment is quoted by Clement of Alexandria:
“He who seeks will not give up until he finds; and having found, he will marvel; and having marveled, he will reign; and having reigned, he will rest.”
Moving to more familiar territory, we come to the “Q” source – a reconstructed text of Jesus’ sayings used by Luke and Matthew. The earliest strata of “Q” dates back to the 50’s, CE. Here is the quotation from the earliest strata of Q, as found in Luke 11:9–10
“And I say unto you, Ask, and it shall be given you; seek, and ye shall find; knock, and it shall be opened unto you. For every one that asketh receiveth; and he that seeketh findeth; and to him that knocketh it shall be opened.”
This is basically copied verbatim in Matt 7:7–8, with Matthew quoting independently from the Q source.
A very similar sentiment is expressed in Mark (who did NOT apparently use the Q source). Mark, as the earliest surviving gospel, dates back to as early as 65 CE. Here it is in Mark 8:1–10
“Therefore I say unto you, What things soever ye desire, when ye pray, believe that ye receive them, and ye shall have them.”
Matthew, in Matt 12:22, copies Mark basically verbatim.
The dialogue of the Savior, is a document which dates to much later (perhaps 120 CE) but which contains portions of a much earlier “sayings” gospel within it – apparently independent of these earlier texts quotes Jesus . It quotes Jesus as saying: “The Lord said to them, “He who seeks […] reveals […].”
Finally, the Gospel of John, while later (90–120), has several citations which are independent of the previous:
“And whatsoever ye shall ask in my name, that will I do, that the Father may be glorified in the Son. If ye shall ask any thing in my name, I will do it.” (Jn 14:13–14)
“If ye abide in me, and my words abide in you, ye shall ask what ye will, and it shall be done unto you.” (Jn 15:7)
“Ye have not chosen me, but I have chosen you, and ordained you, that ye should go and bring forth fruit, and that your fruit should remain: that whatsoever ye shall ask of the Father in my name, he may give it you.” (Jn 15:16)
“And in that day ye shall ask me nothing. Verily, verily, I say unto you, Whatsoever ye shall ask the Father in my name, he will give it you. Hitherto have ye asked nothing in my name: ask, and ye shall receive, that your joy may be full.” (Jn 16:23–24)
So here we have quite a number of independent sources, all quoting Jesus as saying something similar (each having a slightly different “take” on the theme). These sources are as early as 50 CE, perhaps as little as 17 years after Jesus, if not earlier. The fact that they are independent points to the fact that there is an even earlier source, probably oral, dating to the time of Jesus himself. By far the most likely explanation of this is that there WAS a historical Jesus, and that one of the more memorable themes of his preaching was something like “Ask and you shall receive. Knock and it shall be opened”