In the first part of Paradise Lost, Satan finds himself in hell after the failure of his rebellion against God.  Miserable that he has lost paradise, Satan is nevertheless unrepentant and prideful.  He utters the often quoted lines:

Better to reign in Hell than serve in Heaven.

He tells Beelzebub his plan to regain the grounds he has lost.  They conspire to "wage by force or guile eternal war" against their "grand Foe."  To do so, they spot the "dreary plain" earth, and plan to go there to renew their forces and to thwart God's mission to bring forth good.

"Our labor must be to pervert that end,

And out of good still to find means of means of evil"

The temptation of Adam and Eve is the result of this plan to create evil and to attempt to sabotage God's design.