A very precise definition of sanctifying grace might be, “All actions, substance and matter which is directed solely toward inclusion into the divine nature of Christ.”. We observe that the sacrament of baptism includes both actual graces and sanctifying graces. Actual graces increase our virtue, but this is still short of inclusion into Christ.
Sanctifying graces are directed to our ultimate inclusion into the divine nature and person of Christ (CCC 398). We begin our participation into the human nature of Christ because of original sin, which we must overcome and perfect, prior to our inclusion into the divine nature, which is completely free of sin, (recall that sin was never intended).