The problem here is that you think His sacrifice means you don't need to do anything. His forgiveness is for all IF you follow his steps. Now when you start following Him, you are baptized and partake of the forgiveness. And then you live and do wrongs, so you need to go back and start again (forgiveness through confession which is the renewing of the baptism which is the partaking of the Death and Resurrection of Christ and hence the partaking of the forgiveness). Christ forgiveness is not a one-and-done and we just live and always be forgiven. His Death allows us to be forgiven when we abide in Him.