Monotheists, who believe in a God who is the creator - often see no necessity for Jesus.
They assume that God is capable of anything that is possible; so Jesus cannot be necessary; because there is nothing for Jesus to do that God could not do.
This argument is based on the idea of God as defined by attributes, specifically abstract attributes (such as unity, omnipotence and omniscience). Such a conceptualised God is not a Being primarily.
But if we escape the paradoxes of abstract infinites, and instead examine what strict-unitary-monotheists promise to their believers; we will perceive that strict monotheists do not 'offer' what Christians offer.
Christians offer everlasting resurrected life in Heaven - that is, after biological death we remain our-selves, have eternal bodies, inhabit a world of love (and, I would argue, creativity - as 'Sons of God, thus collaborators with God) - and we live with other such persons.
To say that Jesus is necessary should - I think - be understood in terms of what Christians specifically offer - resurrection.
Thus, Jesus is not necessary for creation, but Jesus is necessary if we want to live everlastingly as resurrected selves in Heaven.
If - on the other hand - we do not want what Jesus offered, then Jesus does not have a necessary role!
Monotheists who do not aspire to take-up Jesus's offer of Heavenly resurrection, can therefore rationally assert that Jesus is not necessary (that Jesus was 'just' a prophet, a teacher, an exemplar or whatever).
By this line of reasoning, we can see that Christians are those people who assert that Jesus is necessary, because (in addition) Christians personally desire resurrected eternal life in Heaven - for which Jesus was, and is, required.
