To show the importance of personal sacrifice and total compassion.
The Romans were obsessed with death and with what people did at the time they died. It became a source of entertainment. When they saw how JC and later his followers died (ie in total peace) they were converted en masse.
There is also "the mystery" of JC dying for symbolic sacrifice as a scapegoat etc but this is because the ancient peoples at that time actually thought that way. Being lost for words to explain what happened they used localised Jewish concepts.
Different eras in time and place used different holy concepts and words. We have to untangle it today.