The intercession of Christ, as priest in Hebrews, is not for the forgiveness of sins, nor for sin properly at all, but for mercy and help in time, of need to succor them that are tempted, because all the sanctified are viewed as perfected by one offering. In 1 John, the advocacy is exercised when one has sinned, because there fellowship or communion are spoken of, and this is interrupted by sin. Forgiveness in the sense of non-imputation cannot be sought by one set free in Christ because he does know that sins are not imputed to him. But he confesses his sins, and fatherly forgiveness is given him. Confession goes much deeper into the conscience than merely asking forgiveness.
In 1 John 2 The advocacy of Christ is founded on righteousness and the efficacy of propitiation being already there in Christ. That pardon is plenary on coming to Christ is clear, and (to refer to none else) in Heb. 9; 10, it is largely reasoned out by the Holy Ghost. If not, such sins never could be cleared, as Christ cannot now die over again, and without shedding of blood is no remission. Christ must often have suffered. To make a difference of time is to confound the time of the Spirit's operation in bringing our souls to faith in Christ and His work with the work itself. All our sins were future when Christ bore them. The way in which “once for all,” “forever,” and “no more” are used in Heb. 9; 10 is most distinct and characteristic.