Paradise Lost is about Adam and Eve's fall, the original sin! So it's no surprise that sin is a prominent theme in the poem. Don't forget that we also learn a lot about Satan's major sin (he tried to overthrow God) and a lot about the sins that Adam's descendants will commit. Oh, and Milton constantly reminds us of our sins, or rather of the fact that we are sinners in a fallen world.
Questions About Sin
How bad was Adam and Eve's sin, really?
What about Satan's?
Do only people with some type of religious belief use the word sin? What word do you use?
Was it fair for the whole world to be punished for Adam and Eve's one screw up?
Chew on This
Adam and Eve's sin is especially heinous because they were notified on numerous occasions (by God and by Raphael) about the rules. Such a blatant disregard for a simple rule almost seems worse.
Milton attempts to write a poem about a time when there was no sin; however, the poem is repeatedly dogged by discussions of sin, sinful responses to characters like Satan.