Christ didn't invent some gradation of sins, designating some mortal and other venial.  That was a fabrication by men trying to solidify faith so it could be institutionalized.  Welcome to the history of the institutional church and the basis of the traditions that are the idols of traditionalists.  Best not to think about it, and just pretend nothing has ever changed, and the whole thing sprang into being being on Pentecost, rosary beads, miters and all.