RESPONSE:
Most scholars agree that the verses 9-16 at the end of Mark were probably not written by the original author. Mark's gospel, for whatever reason, ended abruptly at 16:8. Someone found that totally unsatisfactory and added a better ending, borrowing most of the ideas from others. If this is true, then the author borrowed this idea from Luke 8:1,2 where it states: 1 "And it came to pass afterward, that [Jesus] went throughout every city and village, preaching and shewing the glad tidings of the kingdom of God: and the twelve were with him," 2 "And certain women, which had been healed of evil spirits and infirmities, Mary called Magdalene, out of whom went seven devils." (KJV)

Because these verses come immediately after the story of the dinner at Simon the Pharisee's house, where a woman washed Jesus' feet with her tears, people have long connected them. Many assume that the woman who washed Jesus' feet, though unnamed, is really Mary Magdalene. It's a stretch and one that scholars are becoming increasingly uncomfortable with. So for now, let's assume that all we know about Mary Magdalene is that seven devils were cast out of her.

Most commentators agree that this is an indication of the severity of her problem, whatever her problem was. Usually demon possession related to mental illness or aberrant physical behavior, but was not necessarily a morality issue. So there is no reason to suggest that she had previously been immoral. It's simply a way of saying her problem was severe. Now, in point of fact, the "seven" could suggest that she had been cured of seven different illnesses either all at once or on seven different occasions. And sometimes "seven" refers symbolically to "completeness." In that case, the author would be saying that she was totally filled up with demons, and he is then highlighting the remarkable nature of Jesus' cure. We can rejoice in that and be grateful for it, but to go beyond that would be to engage in sheer speculation.

— Mary Jane Chaignot