God is impassible, which means that no one can inflict suffering, pain, or any sort of distress upon him. Insofar as God enters into experience of that kind, it is by empathy for his creatures and according to his own deliberate decision, not as his creatures’ victim. The words “of that kind” are important, for this impassibility has never been taken by Christian mainstreamers to mean that God is a stranger to joy and delight; it has, rather, been construed as an assertion of the permanence of God’s joy and delight; which no pain clouds. How the formula applies to the atoning sufferings of the incarnate Son is a special and open question, on which different views have been, and are, maintained . . . The historical answer [to the question of what is meant by ‘God cannot suffer’] is: not impassivity, unconcern, and impersonal detachment in face of the creation; not insensitivity and indifference to the distresses of a fallen world; not inability or unwillingness to empathize with human pain and grief; but simply that God’s experiences do not come upon him as ours come upon us, for his are foreknown, willed and chosen by himself, and not involuntary surprises forced on him from outside, apart from his own decision, in the way that ours regularly are. In other words, he is never in reality the victim whom man makes to suffer: even the Son on his cross, where “a victime led, thy blood was shed,” was suffering by his Father’s conscious foreknowledge and choice, and those who made him suffer, however free and guilty their action, were real if unwitting tools of divine wisdom and agents of the divine plan (cf. Acts 2:23; 1 Peter 1:20).
J. I. Packer, “Theism for Our Time,” pages 7-8, 16-17.