The problem is what kind of understanding?
How do we know that we have the true knowledge of understanding in our religion?
Many people think they are more understand than the others and even worst they think they are right and others are wrong. This blaming each other becomes so often now adays.
How do we know that someone has already been given “an understanding” in religion?
Simply: having a better faith in HIM and better character. The bigger understanding he/she has in religion, the better he/she appears in faith and character,