Scrooge's business partner, Marley, recommended Scrooge for redemption. This was a form of Marley's penance, to see Scrooge amend his ways and avoid the same fate as he.
UPDATE: Some relevant passages of Marley's visit from Gutenberg Project [highlights/interpretations mine]:
“It is required of every man,” the Ghost [Marley] returned, “that the spirit within him should walk abroad among his fellowmen, and travel far and wide; and if that spirit goes not forth in life, it is condemned to do so after death. It is doomed to wander through the world—oh, woe is me!—and witness what it cannot share, but might have shared on earth, and turned to happiness!”
...[Marley means that every man is responsible to be charitable to every other in life, or, as he, after death]
“I wear the chain I forged in life,” replied the Ghost. “I made it link by link, and yard by yard; I girded it on of my own free will, and of my own free will I wore it. Is its pattern strange to you?”
...[Marley, confined by his chains, explains his pursuit of business to the exclusion of all others made him unworthy of heaven.]
“Or would you know,” pursued the Ghost, “the weight and length of the strong coil you bear yourself? It was full as heavy and as long as this, seven Christmas Eves ago. You have laboured on it, since. It is a ponderous chain!”
...[He asks Scrooge if he knew the weight of his own chain - Scrooge imagines it is long.]
“I have none to give,” the Ghost replied. “It comes from other regions, Ebenezer Scrooge, and is conveyed by other ministers, to other kinds of men. Nor can I tell you what I would. A very little more is all permitted to me. I cannot rest, I cannot stay, I cannot linger anywhere. My spirit never walked beyond our counting-house—mark me!—in life my spirit never roved beyond the narrow limits of our money-changing hole; and weary journeys lie before me!”
“Seven years dead,” mused Scrooge. “And travelling all the time!”
“The whole time,” said the Ghost. “No rest, no peace. Incessant torture of remorse.”
“You might have got over a great quantity of ground in seven years,” said Scrooge.
...[Marley says he cannot pass into heaven until he undoes every link of his chain, and has been working at it already seven years]
“But you were always a good man of business, Jacob,” faltered Scrooge, who now began to apply this to himself.
“Business!” cried the Ghost, wringing its hands again. “Mankind was my business. The common welfare was my business; charity, mercy, forbearance, and benevolence, were, all, my business. The dealings of my trade were but a drop of water in the comprehensive ocean of my business!”
...[Marley says that his "business" was supposed to be charity and good works, not business alone.]
“How it is that I appear before you in a shape that you can see, I may not tell. I have sat invisible beside you many and many a day.”
...[Marley explains why he visits Scrooge - to warn him to amend his ways]
“That is no light part of my penance,” pursued the Ghost. “I am here to-night to warn you, that you have yet a chance and hope of escaping my fate. A chance and hope of my procuring, Ebenezer.”
“You were always a good friend to me,” said Scrooge. “Thank’ee!”
“You will be haunted,” resumed the Ghost, “by Three Spirits.”
“Is that the chance and hope you mentioned, Jacob?” he demanded, in a faltering voice.