There is one God who created this reality. That is the proper meaning of 'one' God - despite that I believe the one God consisted of the dyad of Heavenly Father and Mother.
Beyond this, and apparently since shortly after the death of Jesus Christ, Christians often feel a need to argue monotheism - that there can only be one God, that the oneness of God is entailed, that God is an indivisible unity.
However, my metaphysical understanding is that the oneness of God is a simple matter of fact. The fact that one God created this reality within which we dwell.
There is one God because there is one God.
What about Jesus Christ? There was one Jesus Christ who - again as a matter of fact - was the person who made possible our resurrection and ascension to Heaven.
Before Jesus, resurrection was not possible; after Jesus it was possible (including for those who lived and died before Jesus).
But did The Christ have to be Jesus - or could it have been someone else?
What 'qualified' the pre-mortal individual spirit called Jesus to become incarnated and become The Christ?
My understanding is that Jesus was the first and only pre-mortal spirit who could become The Christ, who could do the job. God always knew there was this job to be done, presumably this was known among the pre-mortal spirits; and it was some time before any of the pre-mortal spirits were ready and capable of doing the job.
Jesus was the first and (at the time) only pre-mortal spirit to be fully-aligned with God's plan of creation - to be willing to do the job in full accordance with the plan.
So Jesus was - as a matter of fact, but not a matter of necessity - the saviour.
But... if that particular personage of Jesus had not been the Christ, then presumably - later on - somebody else, some other pre-mortal spirit - might have been able to do the job.
I regard it as a deep philosophical error that so many Christian, for so long, have felt the need to argue that the oneness of God and the oneness of Jesus are necessary in some kind of ultimate philosophical-metaphysical sense; rather than as matters of fact.
This error apparently came into Christianity quite soon after the death of Jesus - but after the writing of the Fourth Gospel; which is our only written source of what Jesus did and said written by an eye-witness, and one of the closest disciples.
I presume (but don't know) that what became the Fourth Gospel was not known by Paul or the authors of Matthew and Luke - who provided the philosophical basis of later theologians (plus their carry-over of fundamental assumptions from Judaism and/or Greek-Roman pagan philosophy).
By my understanding, the explanations of God and Jesus ought to be much simpler and more common-sensical than they have since become. There is one God because one God made this creation and we dwell in a creation made by one God. And there is one Jesus Christ because he was the first pre-mortal spirit who could do the job and wated to do the job - and now the job has-been-done, so there will never be "another Christ": jesus was the one and only.