The difficulty we have is that most of the time when we think about freedom, we think in terms of spontaneity. So my freedom has to be the absence of external causality upon my acts. But the Christian tradition just doesn't think like that or at least it didn't until the later 17th century. For Augustine, God causes all that is and that is why we are free. It is not in opposition to our freedom, it is precisely the cause of our freedom. What we find difficult to get our minds around is the idea that there could be a freedom which is caused or given to us because we think that the only kind of freedom that we can have is either pure spontaneity or what is sometimes called contra causal freedom. In other words, our freedom to act against a cause acting upon us. And that picture is not, it seems to me, part of the way that Scripture and the Christian tradition has thought. It is that which is often at play in debates about open-theism or whatever - the fear that if we talk about God's sovereignty we must therefore be talking about something which is a subtraction from creaturely freedom to which the answer is no it isn't."
- John Webster, Kantzer Lecture #3, Question and Answer session