Understanding the difference between justification and sanctification can be as important as understanding the difference between salvation and damnation. Rightly dividing between the two is of crucial importance. This is not what saves. This righteousness is not earned or retained by any effort of the saved.
Justification is an instantaneous occurrence with the result being eternal life.
No works are necessary whatsoever to obtain justification. Sanctification, on the other hand, involves the work of the person. Sanctification is not instantaneous because it is not the work of God alone. Significantly, sanctification has no bearing on justification. That is, even if we don't live a perfect life, we are still justified.