In the case that any of John’s readers might have misunderstood what he meant a verse prior, the apostle re-states one of the purposes for his letter. He desires that none who assume the name Christian sin. John reminds us of the person of Christ and the importance of our walk with Him as it affects our witness in daily life, and he places that importance as an argument to refrain from sin. John gives the concession that saints will, sooner or later, sin; therefore he writes to the saint who has trespassed that we have an advocate in Heaven: Jesus Christ the righteous.
Again John refutes the notion that once a person is born again by faith in Jesus Christ that they cannot sin. A Christian receives the imputed righteousness of Jesus our Savior, and in the sense of being judged for our sins (aka being sentenced to Hell) a saint has passed from death to life, John 5:24. We cannot be tried for sins (past, present or future) that Christ died to pay for already. The Father punished sin in Christ when He struck the Son on Calvary’s cross; it is double jeopardy to exact payment from our Sin Bearer, and then to exact it from one whose faith is placed in Christ. Rest assured, Jesus our Lord died for our sins and sufficiently bore the payment such sin demanded, Hebrews 1:3; 1st Peter 2:24.