If what one is describing as fruit - i.e, good works, self improvement efforts, attempts at better behavior, or more obedience to the law, can be done or found in believer and unbeliever alike, then how is that distinctive one from another? It's not! Unbelievers can be obedient to Gods commands can they not? Can't the unbeliever not steal? Can't the unbeliever not bear false witness? Can't the unbeliever love his neighbor as his self? Can't an unbeliever be delivered from drug addiction and alcoholism? Well of course he can. Well if that is the case then can't he be assured that he is actually a believer? No! Why? Because one is not saved nor assured by anything done by them or in them. If the fruit one is boasting in isn't Christ’s death imputed to them ALONE, then it's rotten fruit that even an unbeliever can boast in. It’s pure self righteousness.