The important things we believe or disbelieve, the truth of confessions of faith such as “Jesus is the light of the world” or “the entire Torah [from Moses to Moses via Aqiba, down to the present day] was given by God to Moses on Sinai,” are not dependent on Jesus having spoken of himself in those terms, or on Moses being able to understand the inner connection between the Torah associated with him in the Pentateuch and that same Torah as understood by Akiva.
We believe, we know certain things to be true, or not, based on Gestalt perceptions of great depth and complexity. When we read the words attributed to Moses and his tradents in Jewish tradition, we hear a voice, and the voice is distinct from all others to which we might listen. When we hear the words attributed to Jesus in the Gospels, once again, a voice unlike any other voice can be heard. Within the contours of the voice of Torah or the voice of Jesus, it is possible to make out something of the historical and cultural determinedness of its components. The voice does not become less distinct and less unique in the process of this discovery. On the contrary.
That being the case, it is a priori possible for believer and non-believer alike to calmly distinguish between the narrative identities of Judaism and Christianity attested in their foundational documents and the larger history from which those narrative identities were (and continue to be) abstracted and constructed. The most that can happen is that a non-believer might conclude, as does a believer like Michael Bird, that Jesus did have messianic aspirations and that he self-consciously engaged in a career that inaugurated the kingdom of God as he hoped it and understood it. This would imply that passages like Luke 11:20 and 7:32 reflect the ipsissima vox if not the ipsissima verba of Jesus of Nazareth. The most that might happen is that a non-practitioner of Torah will conclude, and I would, that the entire Torah bequeathed to the Jewish people is an indivisible unity.
Problems arise if and only if one believes that the evidence suggests that somewhere along the line, what once was Torah became something quite else, a perversion of Torah. Or that Jesus was radically misunderstood by his followers. Claims of this kind, however, have a tenuous basis in the evidence at our disposal. It is not the case that such beliefs are totally without foundation. From a point of view within the traditions, on the basis of internal criteria, it is possible to identify perversions, but only against the background of significant continuities. On the other hand, from a point of view external to the traditions, it is easy to stand in judgment of the entire kit and caboodle. There is no getting around that. It comes with the territory. It follows from the basic realities of the sociology of knowledge.
In terms of intellectual engagement, everything hangs on addressing the historical-critical questions biblical studies likes to address in a responsible way and formulating testable hypotheses. And on one other thing: the capacity to enjoy the questions and the nitty-gritty detail in which possible answers to the questions are found.
In order to address the historical questions fairly, it helps to have a low level of anxiety about what answers might seem plausible at the end of the day. For example, if you can’t say, with Michael Bird, that “I would not be bothered at all if the historical Jesus never claimed to be the Messiah” - he can say that because he knows Jesus to be the Messiah in any case - it’s not likely that you will examine the evidence with respect to the question in an even-handed manner, or even want to.
Michael F. Bird, Are You the One Who Is to Come? The Historical Jesus and the Messianic Question (foreword, Stanley E. Porter; Grand Rapids: Baker, 2009). The quotation above is from page 162. The formulation of the part of this post concerned with what needs to be the case for a truth claim like “Jesus is the Messiah” to be seriously challenged is indebted to Bird’s appreciative quotation of a statement by Marcus Borg (p. 162, note 3).