This is one of those texts which can’t be read without a historical introduction, so I’ll try to make it as brief as possible. King Charles II didn’t have a legitimate issue but a whole brood of illegitimate children by various mistresses. (He seems to have the highest score among English monarchs in this particular contest, or he is head-to-head with King John Lackland, I think. Although I suspect Charles’s MO was sometimes that when a lady came to him with a baby, claiming it’s his and he at least vaguely recollected here, he acknowledged the child.) About twenty years into his reign it seemed obvious he wouldn’t have a legitimate heir and thus the throne would be inherited by his younger brother James (the same whose dramatic escape was described by Lady Anne Halkett). It would pose a problem because James was openly Catholic (Charles was kind of secret Catholic sympathizer too, but he had good sense not to flaunt it too much in 17th-c. Britain.) So a lot of people started to lobby for one of Charles’s favourite bastards, Duke of Monmouth, to be made an heir to throne and exclude James, which led to the so-called Exclusion Crisis. The Duke himself encouraged the people who saw him as a better Protestant successor.
Dryden decides to tell this story by using a parallel story from the Old Testament about David’s rebellious son, Absalom. The similarities are really striking, although of course the stories are not 100% identical. Dryden begins noting with a whiff of irony that in the pious old times polygamy was not a sin and so David could, erm, “scatter his Maker’s image” far and wide. He rewrites the biblical story here a bit to fit the contemporary one: Michal, “of royal blood” (the daughter of Saul) is David’s first infertile wife, like Catherine of Braganza was to Charles. But Absalom’s mother was also a daughter of a neighbouring king, not a slave, as Dryden writes and of course in the biblical story sons by other wives could inherit the throne too. Absalom is handsome, brave and favoured by his father. The Jews, having it too good, start to feel restless under David’s mild rule. They effectively made David a king, after getting rid of the weak son of Saul (referring to Richard Cromwell, Oliver’s unsuccessful son), so why not unmake him and start a republic again? So far the vast majority of people are reasonable, but “the careful Devil” is always on the look-out for an opportunity.