What is the social significance of the heroine’s marriage to Mr. B.? Why was it possible for certain male readers to identify with Pamela?

Pamela and the squire discuss the way their marriage will be treated prior to the ceremony. They realize that there will probably be all fall out because he's marrying beneath his station......... a serving maid no less.

His sister arrives, going on and on about how inappropriate the marriage is, and after finding out the nuptials have already taken place exposes her brother and his mistress. The Squire confesses all to Pamela, although he's furious. Later, when he's calmed down, he very sweetly (and I'm being sarcastic) explains the working of an upper class marriage. He lectures her on the 'rules' she'll have to abide by.......... just because. He can do whatever he likes.

As for the male readers identifying with her.......... your guess is as good as mine.