Okay, Zev’s “hijack” is actually not one, on the “substitutionary atonement” model for how Jesus’s death brought salvation. Short explication of that follows:
First, since A&E sinned, all mankind has been brought into the world and raised by sinners, and hence cannot escape the taint of this ‘original sin.’ (Theologians discoursing on “original sin” are amazingly opaque, even compared to their normal writings, but suffice it to say that whatever it is, it’s inherent in being human since the Fall, so nobody can escape it – and it taints one so that “actual sin” is inevitable, so God is just in judging by it.)
Second, by God’s covenant with Abraham and later with the Jews, He established sacrifice as the means of atoning for sin. His rules, His decision as to what the escape clause is; don’t argue it, okay?
Third, since every individual man (and woman) carries upon him/herself the burden of the sins he/she commits and the taint of original sin, forgiveness for all is impossible by a single act, unless it is God who commits that act. But it must be man who atones for man’s sins.
Therefore, God the Son took on human form, and became truly God and truly man in one Person, so that He might take upon Himself all the sins of the whole world and atone for them through His self-sacrifice, giving Himself up to be crucified. Only in this way could God’s mercy in forgiving sin and His justice in meting out the punishment proper for it be reconciled.
There are other understandings of the Atonement. In particular, one that has some acceptance is that sin inevitably causes a separation between God and man – it’s the essence of sin that it be that; the individual sins are only instances of how that wedge between God and man is driven in. But Christ unites man and God in one through His Incarnation, and through His sacrifice of Himself reconciles God and man, for both died on the Cross. By His Resurrection and sending of the Holy Spirit He provides a new life in which man has access to union with Him and through Him with the Triune God.