a. 1 John 2:l tells us not to sin but virtually gives license to sin. Jesus as your lawyer will "fix your ticket" with the Judge, the Father.
b. 1 John 2:l tells us not to sin, like our insurance company tells us not to have an accident. But you're sure to slip up sooner or later, so make certain you are "covered" by the Advocate's policy. Many times the idea our people have is that Christ is our Lawyer pleading with the Judge to let us off. We cannot expect more than victory over "known sin." Participation in unknown sin implied to be inevitable until Jesus comes. (Biblical examples of unknown sin are the crucifixion of Christ and the perpetuation of Laodicean pride).
c. In context, 1 John 2:l says that for His people to stop sinning is the purpose of His sacrifice. And this is to become effective when they grasp the principle of corporate guilt--and see their relationship to "the sins of the whole world." Thus John's concern was for the work which the cleansing of the sanctuary is to do. The Father, the Son, and the Holy Spirit are united to enable believers to over-come as Christ overcame. This of course includes victory over all sin but is never consciously realized or claimed. (This is not fanatical "perfectionism" so-called, not self-centered, but is entirely by faith).