What does the Confession mean when it says God is immutable? Does it mean God is utterly impassible? Can God suffer? What do these terms mean? Sam Renihan writes:
God is simple. He is all that he is in one pure simple act. He cannot suffer in either sense because he cannot be perfected, nor can he be diminished. God has no parts. You can’t add him up or subtract him. God has no passions. He does not have emotions that can be acted upon or provoked by the creature. The creature can neither increase God’s love nor decrease his wrath. God’s love and wrath are effected, that is, they come from him to the creature. They are not affected, produced by the creature’s action upon God. As creatures we change in our relation to God, and his works upon us our [sic] various, but God never changes. We can go to him and trust that at all times he is perfectly loving in the fullest sense (beyond creaturely comprehension).
Check out the original post for some added material from John Norton and Samuel Bolton: Passivity and Suffering | Particular Voices.