A Believer becomes new creation at the point of salvation, but that new man does not automatically have control over the old, but still present, sin-nature. Sanctification is the process of putting to death that old sin nature so that Christ can reign in us… a Believer with God's Word incorporated his/her heart is Word-driven and Spiritually centered, free from the power of sin.
Jesus' resurrection… gives us hope that we too can live our lives unburdened by sin/sinfulness/the sin-nature. We have a hope for the present, for our day-to-day walk, that sin does not have to rule over our lives: Jesus' resurrection means we are free.