Given that no pope has resigned in 600 years, and that even that precedent is distinguishable, today’s unusual events call for an explanation. Some possibilities:
1. Benedict has a desired successor in mind, and has reason to believe that person is more likely to become pope if Benedict resigns now.
2. Benedict is in ill health in some way that might affect his mental abilities, perhaps causing him to worry about taking a mistaken official action as his mental state declines.
3. Some form of blackmail, explicit or implicit, is afoot. Perhaps there are more potentially damaging revelations about Benedict’s involvement in the Church’s recent scandals, but reason to believe that resignation will keep them quiet.
4. A conscious desire for a change in Church policy with respect to papal resignations, possibly motivated by 1 or 2. In variation 1, Benedict might fear the future radicalization/liberalization of the Church and therefore believe that it should transition to a system of papal resignation and papal influence over one’s successor. In variation 2, the increasing extent to which physical health can be prolonged to outlast mental health necessitates a new way of dealing with papal infirmity.
5. Divine inspiration.