Samuel Richardson's Pamela was such an enormous success when it was first published that it was inevitable that it would soon be parodied. And so it was, with parodies pouring from the press on a regular basis. Arguably the most famous of these is Henry Fielding's Joseph Andrews.
Fielding had already parodied Pamela in An Apology for the Life of Mrs. Shamela Andrews, or Shamela for short. It was published under a pseudonym, and Fielding never publicly took credit for the book. However, a year later, he gladly put his name to Joseph Andrews, a more substantial and enduring piece of work.
As Joseph Andrews is a parody of Pamela, it's inevitable that it shares a number of similar themes. The most important of those themes is virtue. In Pamela, Richardson employs a very restrictive concept of virtue, which he seems to regard as synonymous with female chastity. Fielding, on the other hand, treats the concept in the wider Aristotelian sense of moral excellence.
Whereas Richardson's treatment of virtue is somewhat over-earnest, Fielding adopts a more playful, humorous posture, poking fun at the moral conventions that his fellow author cherished so deeply. We can see this displayed in Joseph's highly moral determination to save himself for his beloved Fanny sees him adopt the kind of attitude normally attributed to chaste, respectable young ladies like Richardson's Pamela.
This is meant to be amusing, as is the way in which the virtuous Joseph and his equally virtuous companions are routinely exploited by the unscrupulous characters that they meet. Even so, Fielding avoids Richardson's somewhat crude division of humankind into the virtuous and the vicious. Although Joseph Andrews is a humorous piece of work, it makes the serious point that, unlike Richardson's black and white portrait of humanity in Pamela, people as a whole are really rather complicated.