Farnham sums it up well. Mephistopheles collects the souls of those already damned - but he cements their status by giving them a final choice and makes sure that they understand that they are gaining great gifts in life and great damnation in death.
That is what many in D.C. have done - made that choice to gain great wealth and power. In the end Faust's students call upon him to call upon God and repent but Faust is certain that salvation is not available to him.
All Christians should read Faust.