Paradise Lost is an epic poem written by the seventeenth century poet John Milton, in which the poet symbolically describes the fall of man beginning with the fall of the angels.
Paradise Lost consists of twelve sections, or “books”, written in blank verse. The first version of Milton’s epic poem was published in 1667, and was edited and revised by Milton in 1674 when he turned initial ten books into twelve.
After they are banished from heaven forever Satan is quite specific and direct to Beelzebub, "the lord of the Flies", Satan Tells him that their only purpose will be: to do ill will, to do evildoing,
So, the answer to this question is: to do ill will.