No one who continually sins does so as a result of a relationship with Christ. True fellowship with Chirst cannot result in sin - this is part of John's defense against the claim that the gospel gives people an excuse to do wrong. A believer is marked by a changed life. It will involve some level of growth, known as sanctification, and is expected to be noticeably different from that of an unbeliever. Though every believer is a work in progress, every believers life should show a noticable difference in living a life that beomes more like Christ.
1 John 3:6
But if we confess our sins to him, he is faithful and just to forgive us our sins and to cleanse us from all wickedness. NLT