Free will and ethics
Spinoza's argument that God is not "free" to change stuff as the whim might occur to him is presented as a projection of a human process on to the Creator. Men ponder alternatives to achieve various ends. To depict the God we are in as sharing the same conditions that we do is presumptuous.
The funny thing about the presumption is that we use it conceive an agency in ourselves. We take the model of coercion and liberty that we must navigate to live and turn it into something beyond our experience.
The lesson on humility is not directed toward saying everything must be as it is as a matter of predestination. That sort of thing is beyond us. The freedom we experience is not something we
have, like a property or a hand tool. The difficulty surrounding the possibility is a feature, not a flaw.
From the point of view of understanding causes, this from Ethics, Proposition 8, Scholium 2 points to what is being resisted:
Those who do not know the true causes of things confuse everything. They have no more intellectual qualms about conceiving of trees talking than of people talking. They as easily suppose that human beings are formed from stones as from semen. They imagine any form being changed into any other form. Similarly, people who confuse divine nature with human nature readily attribute human emotions to God, especially so long as they also remain ignorant of how emotions are produced in the mind.
-Spinoza: Ethics: Proved in Geometrical Order (Cambridge Texts in the History of Philosophy) (pp. 7-8). Cambridge University Press.