[Note: I use the phrase "tetralemmic polarity" in various places, referring to the idea described in the essay of that name. But it is generally used more or less tangentially, so I think the following can for the most part be read independently.]
The Doctrine of Divine Simplicity (DDS) is a claim of classical theism (the theism of most all pre-modern theologians, from the Greek Fathers and Augustine to Maimonides and Aquinas). The claim is that the First Cause (what I call "fundamental reality") cannot be a composite, that it cannot have parts. For if it did, it would then be explainable by the joining of those parts, and so not be fundamental. I concur with this argument, and indeed see it as affirming nondualism, from which classical theism is only a step away. (That step is that classical theism needs to abandon the idea that God is unchanging for the idea that God is the tetralemmic polarity of permanence and change. But that is not our concern here.)
What the DDS implies is that any attribute one ascribes to God must be numerically identical to any other attribute. Further, it implies that God is that attribute, rather than a being that has that attribute. For example, God is not a being that knows, rather God is Knowing. Not a being that Loves, but Love itself. And it means that, for God, to Know is to Love. Likewise for (not a complete list): Intellect, Power, Will, and Feeling.
The capital letters used in the preceding paragraph are a traditional means of warning the reader that, for example, the Intellect that is God can only be understood as analogical to human intellect. However, I shall argue that the difference between our intellect and God as Intellect is not analogical, rather it is the same, but in our case in various ways extremely limited. The argument is straightforward. For God, a thought is an act of will is a feeling etc. All things (including ourselves) are thoughts of God, maintained in existence by God continuing to think them (a standard claim of classical theism as well). There is no point where a thought of God can somehow split into separate ontological categories, like a faculty of thinking separate from a faculty of willing. Rather, throughout reality, a thought is a feeling is an act of will. It is only our limitations that have caused us to have separate words. In semantic parlance, the three words (thinking, feeling, and willing) have different connotations but identical denotation. How this came about is an interesting question, see here for some thought on the matter.
What this means is that local consciousness (like mine or yours) is just as "simple" as divine Consciousness. Or rather, it is ontologically simple, but made enormously complex by being local, or limited. Take the question of will. (Note: I consider the phrase "free will" to be redundant -- if it is not free it is not will. And while I'm at it, I consider the phrase "blind will" to be oxymoronic. Since it is Consciousness that is Will, there is no "unseen" act of will.) To will is to think, and to think is to will. Since we think, we obviously have will. But not so fast. Can we truly say that it is me that thinks? Given the large quantity of uncontrolled thinking we experience (what Buddhists call "monkey mind") it is not obvious that this is me thinking. On the other hand, there seems to be controlled thinking as well. If nothing else, there is the control exercised by being able to stop, at least momentarily, monkey mind. But there is more, with the clearest example being mathematical thinking.
Consider, first, that when God thinks, that which is being thought is being created. On the other hand, if I think of, say, a house, no house is created. But when I think of a Euclidean triangle, that thought is a Euclidean triangle. The following is from Owen Barfield's What Coleridge Thought (p. 15 -- internal quotes are Coleridge's words):
"Mathematical lines, points and surfaces are "acts of imagination that are one with the products of those acts." And this remains true of the figures constructed with them. A geometrician draws three meeting lines on a slate; but the 'triangle' which he then sees merely represents to him (and imperfectly) an ideal figure he has first had to produce by an act of thought or (it is practically the same thing) an act of imagination.
" "[the] spirit in man (that is, the will) shows its own state in and by its acts alone; even as in geometrical reasoning the mind knows its constructive faculty in the act of constructing, and contemplates the act in the product (that is the mental figure or diagram) which is inseparable from the act and co-instantaneous.""
In other words, when doing a mathematical exercise, we are, inseparably, thinking and willing. (And feeling, though for many that is not so obvious, but is why mathematicians speak of the beauty of mathematics). We are creating, or re-creating, and maintaining in existence, mathematical objects. The reason this is not the case when we think of a house is that we are incapable of holding in mind every last molecule of an actual house. Nevertheless, what is the case with mathematical thinking does carry over into other disciplines, such as science and philosophy. The key word is 'discipline'. While I am not creating gravity when thinking through a theory of gravity, I am creating (or re-creating) the theory, to do which takes training. This training is learning to exercise one's will.
An objection might be raised that one cannot specify that there is an "I" that chooses to take up, say, a mathematical exercise, or that continues to choose to keep one's focus on it. One response to this objection is to note that it is the case that whatever I do is at the same time what God is doing, since I am simply a localization of God. But this answers the objection. Whether one says it is "I" or God that is thinking the Euclidean straight line, it is here at this localization that it is being thought. Which just means that it is "I" doing the thinking.
A more complicated response covers the more general topic of whether it makes sense to speak of a 'self' at all. I hold that it does, but only when using the logic of tetralemmic polarity. I won't do it here, but basically it amounts to showing why one cannot say -- given a specific localization of consciousness -- that it is a self, that it is not a self, that it is both a self and not a self, nor that it is neither a self nor not a self. In sum, the question of "Do I will" is a variation on the question "am I God", with the answer "I am in a tetralemmically polar relation with God".