I don’t mean to be entirely dismissive, but for me this question verges on absurd. Not that I haven’t encountered it before — in fact my first interactions with Christians who were striving to convert me centered around the various approaches to evidence or “proofs” concerning the person of Jesus and his miraculous acts. In the context of many Christian believers I met, it was these proofs that justified their beliefs…and so I think they assumed that the copious amounts of what they considered persuasive evidence would rock my world (though for some I suspect this was more about reinforcing their own self-justifications). But there was always something…well…that felt like a serious falling short on this particular road to any meaningful conclusions about Jesus and the Divine. I couldn’t quite put my finger on it…and so I shrugged off this rationalistic approach, along with many of these overeager evangelists.
Then one day - at the encouragement of a friend - I decided to read the Gospel of John. And the more I read it, the more a lot of things began to fall into place for me — in terms of understanding the early Christian message, and also understanding myself and what was really important to me. This has to do with what I would call “the felt reality of truth.” To know something in one’s bones in a non-rational but nevertheless profoundly persuasive way. I didn’t know Rumi at that time, but he spoke to this experience artfully:
“Intellect is good and desirable to the extent it brings you to the King's door. Once you have reached His door, then divorce the intellect! From this time on, the intellect will be to your loss and a brigand. When you reach Him, entrust yourself to Him! You have no business with the how and the wherefore. Know that the intellect's cleverness all belongs to the vestibule. Even if it possesses the knowledge of Plato, it is still outside of the palace.”
And of course the non-rational gravity well that the Gospel of John describes is all about agape — Divine love. Something Rumi and Hafiz also expounded upon extensively, and their writing would later me into “a felt reality of truth” in much the same way that the Gospel of John did. Some other Christian and Jewish texts have had a similar effect — Psalms, Ecclesiastes, The Shepherd of Hermes, The Gospel of Thomas - but the Gospel of John really grabbed me in a way that was meaningful…and enduring. Because it spoke to my heart in a language that my heart knew, but my mind…well…it didn’t really understand anything at all.
In any case, this message of love “rang true” in ways that invited relationship with the Divine. And so I embarked on a journey to intimately know “the enigma in the mirror;” to explore and eventually embrace a deep and abiding love affair with God. And without the Jesus described in the Gospel of John — without the words and deeds attributed to him in that book — I would not have experienced this transformation. I would certainly still be a spiritual person, indeed I would be a mystical person, and perhaps even a person who learned over time how to be more compassionate and kind to others…but I would not have become devoted to love itself. And I don’t think I would have been as empowered in this journey (in a spiritual sense) to seek the good of All.
So for my experience of faith (and I do not mean belief, but Faith as an Intentionally Cultivated Quality of Character), this Quora question is a mighty distraction from what I feel is essential - from what I now discern to be important and vital in my own religious experience. And, further, I would say that I “know” (in the sense of gnosis and sophia) the spiritual truth of love as an “absolute certainty.” How do I know? Because I was willing to practice, as best I could, the mindset, attitude and relating to others that the story of Jesus conveys — and because I was willing to invite holy spirit to assist me in these interior and exterior efforts.
In this context - the context of experiential certainty of transformative power - “personal theories” about Jesus of Nazareth are intellectual exercises, distractions that do little more than inflame egos into defending or assailing them. Perhaps, as the question poses, such theories can form the basis of a “rational discussion” that appeals to some - perhaps to a fruitful dialectic. But for me it is like trying to explain what it feels like to jump naked off of a cliff into an icy lake…using math, when it really should be poetry.
My 2 cents.
From Quora: https://www.quora.com/Given-that-we-cant-know-for-absolute-certainty-what-are-your-personal-theories-regarding-the-story-legend-truth-of-Christian-figure-of-Jesus