The doctrine of divine impassibility is a biblical, catholic, classical, and confessional doctrine of the Christian church which states that because God is simple, infinite, eternal, and immutable, he cannot undergo any change in state of being, or be acted upon in any way. The Reformed confessions of faith express this by saying that God is “without passions.” This negation separates the being of God from an aspect of creaturely existence.
To understand divine impassibility, therefore, we have to study the divine nature that requires such a negation and the creaturely existence being denied of God. Many authors, far more capable and knowledgeable than myself, have dealt with the first part, arguing convincingly that the divine nature cannot be acted upon by anything or undergo anything. It is my goal to address the second element of this question, often untouched in these discussions, passions and affections in the context of the human nature. As we improve our understanding of the imperfections of our creaturely nature, we will improve our understanding of the perfections of God’s divine nature.
Man’s nature has parts—body (material) and soul (immaterial). And it has faculties seated within those parts—the mind, the will, and the passions or affections. The affections bring together the parts and faculties of the human nature. Affections are motions of the mind and will relative to perceived good and evil.
In other words, as a given person goes through life, their mind interprets the world around them and regards various objects as good or bad. If perceived as good, the person is drawn to those objects. If perceived as bad, the person is drawn away from those objects. These motions are the affections, and can therefore be sorted into two opposite lists.