MArley was allowed to return to do a good deed and warn Scrooge that he(scrooge) was making teh same mistakes as Marley and the out come would be worse as Marley points out he (Marley) will walk the earth for all eternity in torment for not making mankind his business
Jacob Marley. Marley foretells of 3 others who will help Scrooge
Marley tells Scrooge that he will be visited by three Ghosts the first as the clock strikes one in the morning
Marley tells Scrooge to expect three more spirits to visit him that night.
Marley's ghost, the first of four, visits Ebenezer Scrooge.
To warn Scrooge to change his ways and be nicer or kinder to other people, or else Scrooge would end up like Marley(lonely and hated).
Marley was very much like Scrooge in life. However, Marley having suffered seven years of torment in the after life sees that that Scrooge is also destined for everlasting torment after his death and he seeks to redeem himself if only slightly by warning his friend Ebenezer
When Jacob Marley came to visit Scrooge didn't believe that it was really Marley. So Marley showed Scrooge if he didn't change his ways that Scrooge would bear himself in chains of his wrong doing.
At mid night
Scrooge's dead business partner was Jacob Marley. He was the 1st ghost to visit Scrooge.
Marley foretold three ghost would visit and all three did
Scrooge reacted with shock and disbelief when Marley's ghost first appeared to him. He initially thought it was a hallucination brought on by his own guilt and fear. However, as Marley began to explain his purpose and warn Scrooge about his own fate, he gradually accepted the reality of the situation.
Marley infers sthat he himself was always near Scrooge but he could not be seen however, due to the significance of the situation he had made every effort to redeem himslf a little by helping Scrooge