I have had great difficulty in finding an acceptable and effective metaphor to comprehend Christ's atoning sacrifice.
If YOU personally are satisfied with your current understanding of this matter, with what Christ did, why and how - then I would advise you NOT to read my essay; since it could only annoy you, or perhaps (much worse) confuse or damage your understanding.
This is for those who need to explore different ways of understanding what is without question the greatest fact of Man's existence.
The Copernican inversion in this explanation is that I try to understand the work of Christ in terms of what Christ needed to do in order to be able to save Man.
The fact of Christ's incarnation implies that it was necessary; the fact that the incarnation was necessary implies that without it Christ could not save Man.
In other words, prior to the incarnation there was something lacking in Christ's ability to save Man; and as a result of the incarnation Christ gained the ability to save Man.
(God the Father, it should be noted, could not in and of Himself, save Man. Without the incarnation man could not be saved.)
The incarnation increased the capacity of Christ. So the work of Christ can be understood in this sense - opposite from the usual approach - of what Jesus Christ needed to learn some vital capacity - or needed to experience something crucial - in order to be able to save Man.
Christ's incarnation and atonement can therefore be conceptualized as that being born, living, experiencing joy and temptation, suffering, dying, being resurrected and ascending to Heaven... some or all of this was necessary such that from that point (after those experiences) Christ could save us.
So what was crucial? What was the focus of the incarnation? To save us from sin and death. Revelation tells us it was his atoning sacrifice - his suffering of the sins and pains of Man - and his death.
So, it seems that Christ's ability to save us from death and sin depended upon Him personally experiencing and learning from His own suffering of the consequences of Man's sins; and suffering too the death of His mortal body.
By Christ's suffering of all possible sin and suffering including death, He became capable for saving us from them.
His gift was his own voluntary and chosen suffering needed in order that he might learn and become enabled to save us - this being done for us, from Love.
Christ did not - by this account - remove sin nor absorb it nor even counteract it; nor did he suffer on our behalf for reasons of justice; instead Christ suffered the sin and death of each and every Man, and so He knows us fully, and knowing us, therefore becomes able to forgive us - each one individually.
So to understand why only Christ can save us - we need to understand that God the Father could not save us; and that before His incarnation Christ could not save us - but that because of His divine experience of incarnation and death Jesus Christ is uniquely able to save us - and that all of this was done for Love.
So we are saved, we have been saved; but in order for this to be enacted requires that we accept what has been done as Good; and this is what it means that we must Love God (whose plan this was from the first) and acknowledge Christ as our Saviour; and this entails that we Love our fellow Men - because the plan was for all Men (not only for us as individuals).
The above is a "Copernican inversion" of the usual theology, because it is a 'God's eye view' and a 'Jesus Christ's eye view' (inverting the usual human-centred perspective), concerning what needed to be done to save Man from sin and death.