Lady Philosophy asks Boethius to “imagine a set of revolving concentric circles” in her effort to explain how Providence and Fate relate to one another. It is extraordinary how Boethius evokes a visual image to try and explain a deep and perennial mystery. The innermost circle is closest to “the simplicity of the centre” which is equated to the “high citadel of oneness” which is Providence or “Divine Reason.” Providence is also equated to the “Primary Intelligence.” Due to it being equated with Divine Reason, Providence does not itself orbit anything. It does not move. It is essentially the Unmoved Mover. The closer an orbit is to the simplicity of the centre, the more that thing which is the circle is freed from Fate (or “above the chain of Fate”). It seems to me this is essentially “rest”.
Fate is what governs (in varying degrees) anything at all which is subject to change. Fate is “the ever-changing web, the disposition in and through time of all the events which God has planned in His simplicity.” There are multiple concentric circles which represent all things subject to Fate in varying degrees. The orbits of Fate become more subject to change and more chained to Fate the further away they are (or move) from the stable and simple centre (“whatever moves any distance from the primary intelligence becomes enmeshed in every stronger chains of Fate”).
Providence, while being the stable and simple centre, also “includes all things at the same time, however diverse or infinite.” Fate is the particular, local, and temporal change relating to every specific thing. So, the relationship between Providence and Fate may also be expressed as the relationship between “Being and Becoming,” “Eternity and Time,” or “Intelligence and reasoning.” I’m reminded of the famous image which (I think?) is first described by Plotinus (or perhaps Aristotle?), but in a simple form is expressed by many others. For example, “God is an intelligible sphere, whose center is everywhere, and whose circumference is nowhere” (Alain of Lille).
Whereas Fortune does not explicitly figure into the description of Providence and Fate, it seems to me that Fortune, relating to the ultimate reality of Providence and Fate, is the way human beings perceive the changes of Fate (Fortuna is our experience of change personified). “Ignorant men look on with wonder at his actions” and attribute to Fortune what we perceive as the rise and fall of our circumstances, the change between joy and suffering etc. As Fortune is our perception of the changes of Fate, and all Fate is governed by Providence, “All fortune is certainly good.” How this works with the truth of free-will is an inevitable follow-on discussion which occurs in Book V.
Consider this quote from Hebrews 12
Yet once more I will shake not only the earth but also the heavens.” This phrase, “Yet once more”, indicates the removal of things that are shaken—that is, things that have been made—in order that the things that cannot be shaken may remain. Therefore let us be grateful for receiving a kingdom that cannot be shaken, and thus let us offer to God acceptable worship, with reverence and awe, for our God is a consuming fire.
All that can be shaken will be shaken in order to reveal that which is stable and unshakeable. There is a bit of that going on here I think, in how Providence (unshakeable) holds Fate (all that can be shaken) within itself for a higher purpose.