My position is that Jesus brought us the new possibility of resurrection to eternal life in Heaven - a Heaven that (unlike this mortal world) is a place of beings motivated by freely-chosen love; and therefore a situation free from entropy/death and evil.
Heaven is therefore a Second Creation.
And Heaven is a place where Men are wholly Sons of God, therefore not just observers or enjoyers; but active participants in divine creation.
Before Jesus this was not possible. Jesus's life, death and resurrection was necessary for this to happen.
And this is why Christianity is unique, and itself necessary for those who desire for themselves resurrected life in Heaven.
(It follows that Christianity is Not necessary for those who desire something else than resurrection and Heaven.)
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So why does mainstream, orthodox, traditional Christian theology fail to acknowledge this?
I think there are two main reasons.
One is the commitment to making Jesus's Jewishness into something theologically necessary. The other is the commitment to defining God monotheistically and as omnipotent.
When theologians are committed to Jesus's necessary Hebrew ancestry (including that he was the Jew's prophesied Messiah, the rightful King of the Jews on earth); then they are compelled to integrate the Old Testament with the Gospels (including the Fourth Gospel "John" which ought to be regarded as primary).
Compelled, therefore, to emphasize the continuity with Jewish monotheism, and a specifically racial (and this-worldly) account of Jesus's work and achievement (because the Messiah was the rightful King of Jews in this-world).
If Jesus is seen as part of an ancient and tribal process of a monotheistic God; then this apparently pushed some early Christianity theologians (whose view became dominant, then mandatory) to abolish Time from Christianity - which led them to elide, ultimately deny, the difference before and after Jesus.
(Because when Time is regarded as ultimately, divinely, unreal - then all Time is one, and there is no before or after: that sequential view of history is just an illusion from the mortal perspective.)
Instead of being something newly possible, Heaven became regarded something more like a return - resumption of a paridisal state of blissful contemplation, worship, and joyful gratification.
The difference between Paradise and Heaven is that Paradise is essentially static.
Paradise may be cyclically conceived (like the cycle of fights and feats in Valhalla), or a state of suspended-Time - with the abolition of Time.
But in Paradise nothing essential changes: Paradise is not going anywhere - it Just Is.
Whereas Heaven is properly understood as a transformation of this mortal life -- to become a life for all rooted wholly in love, having eliminated entropy/death and evil - such that love and all creation become everlasting, while remaining dynamic and growing.
Heaven is a continuation - in a new form - of divine creation (or rather divine create-ing).
Thus the term Second Creation for the work of Jesus...
Thus Heaven is open-ended, dynamic, and changes creatively - eternally.
Jesus can only bring something wholly new insofar as Jesus is a divine being distinct from God the primary creator.
If there must be One God, and Jesus is divine; then Jesus is merely a part of God (as with the paradoxical-mystical mainstream conceptions of the Holy Trinity) - and since the One God has always been, and was primary creator: then Jesus is nothing new.
If God is an Omni-God - omniscient, omnipotent, omni-present, impassible etc - then Time must abolished, and God must live outwith Time - therefore Jesus is nothing new, because there is nothing new.
From the above it can be seen that (unnecessary, mistaken) decisions about metaphysical assumptions - presumably introduced by some early Christian, and probably Jewish, theologians; had the effect of rendering Jesus Christ theologically dispensable.
(Whatever bald assertions to the contrary are so strenuously, but incoherently, asserted!)
This; because whatever Jesus did was also regarded as done by God the primary creator; and Jesus could not be separated from God the primary creator - therefore Jesus the mortal Man was inessential.
Indeed, because Time is ultimately illusory, whatever Jesus did was actually already-done before Jesus was conceived and born!
Consequently, through these and other stream of thinking that converged theologically; Jesus's work and transformative achievement was blurred, distorted and diminished; and this was done (I infer) in order to fit with Hebrew and monotheistic theological assumptions: assumptions that soon became theological dogmas.
