Simply to stop sinning (even if that were possible, which it isn't) doesn't solve the problem. That fact that one has ever sinned at all at any time makes the atonement of Jesus Christ necessary. Any sin, however minor, makes one unclean and the only thing that makes the sinner clean is being washed in the blood of the lamb of God who is Jesus Christ. Repentance creates a change of heart but it doesn't change the fact that sins have occurred prior to repentance. The atonement of Jesus Christ has effect when one keeps repenting as process, which is what makes the individual 'one' with Jesus Christ which in turn enables grace and salvation. Since repentance is a process, we will still need the scriptures to show us the path so that we can know how to repent and what to repent of.
Picture a path leading to eternal life. Running alongside this path is an iron rod. The iron rod is the word of God. The path is covered by mists of darkness which are the cares and temptations of the world. Only by holding onto the iron rod can the individual safely navigate the path and reach eternal life.