What distinguishes the death of Jesus is that (if Christianity is true) it was the voluntary death of a sinless man. Since physical death is a consequence of sin, the death of Jesus would have been undeserved (and therefore its allowance would have been immoral) unless he received adequate compensation for what happened to him. His compensation, as it turns out, is that the merit of his life is applied to those who choose to align themselves with him. That, at least, is one way of understanding the atonement which appears to account for all of the biblical data on the topic. It also explains why the death of Jesus must be accepted by the believer in order for it to perform this function for them. Just as it is wrong to do something to someone else without their consent (provided they might object to having it done to them), so too would it be wrong for Jesus to have his merit applied to others without first acquiring their consent. Unfortunately, not everyone gives this consent, and thus the merit of Christ is not applied to everyone.