Fielding admired honesty, integrity, simplicity, and charity, believed that virtue is seen in an individual's actions, but recognized the difficulty of making moral judgments. How is the reader to judge the postilion who gave Joseph his coat but was later convicted of stealing chickens, or Betty, who is charitable and promiscuous? Good men do not necessarily have harmonious relationships or understand each other, as is seen in Adam's interactions with the Catholic priest and the innkeeper previously hoodwinked by the "generous gentleman."
Fielding is asking us to use our own judgement, and pointing out to us that we are neither all “good” or “bad”. There is a tension set up between appearances and reality.
For example Parson Adams is charitable in all that he possesses, and would risk his own life to protect his students and friends. When Joseph Andrews encounters him in a tavern he is genuinely glad to see Parson Adams, which testifies to the greatness of his philosophy of charitableness. Parson Adams likes some of the more worldly pursuits of food and drink also but this echoes the point I made above. Look at the difference between Parson Adams and Parson Tulliber. The latter is greedy and gluttonous while the former enjoys his food.