Yes, of course what happened at the cross was vitally important, but if Jesus was simply going there separate from us, it would have resulted in religion.
Oh wait!! That is exactly what many people think. They weren't told that as a result of the incarnation, what Jesus did, he was doing for us us! Not in a separate sort of way, but as the Son of Man he represented all mankind. So whatever happened to him was happening for the whole of humanity!