Will and understanding are one and the same
Formal Statement
Will and understanding are one and the same thing. There is in the mind no volition — no affirmation or negation — save that which an idea, inasmuch as it is an idea, involves.
In Plain Language
This is the positive payoff of denying free will. Will is not a separate faculty that stands over your ideas and decides which to accept. To have an idea just is to affirm it (unless a stronger idea overrides it). When you grasp a proof, you do not then separately "choose" to believe it — the understanding is the assent. This means freedom cannot consist in unconstrained willing, because willing is nothing over and above understanding. If you want to change what you affirm, you need to change what you understand.
Why This Follows
Step 9 (df-09) denied absolute free will. This step explains why: will is not a separate thing that could be free or unfree. It is identical with understanding. Each particular idea carries its own affirmation. This collapses the traditional distinction between intellect and will that was supposed to explain error and freedom.
Freedom cannot mean unconstrained willing, because will just is understanding.
Connected Concepts
If believing something is just understanding it, what happens to the experience of "choosing to believe"? Is it real, or an illusion generated by incomplete information?