Thomas Weinandy has an excellent book entitled Does God Suffer? thoroughly defending the doctrine of Impassibility. I'm going to offer some thoughts from it and on it over a couple of posts.
In Chapter 1 he covers some of the background and terrain of the debate, including the desire for a passible God (ie, a sympathetic one), the thought of people such as Moltmann, the biblical picture of God as passionate, emotional, and involved, and the overwhelming tendency to attribute impassibility to Hellenic philosophical thought in the Early Church Fathers. Nothing too new here.
Chapter 2 offers some great insights though. Firstly, Weinandy helpfully distinguishes theological problems from theological mysteries (p30-31, drawing on Gabriel Marcel). A problem can be clinically analysed, systematised, and 'solved'. A mystery on the other hand, cannot be exhausted. We can say much about the Trinity, for example, and some things wrongly so, and many things wondrously and truthfully so, but we cannot exhaust the Trinity. So too with Christology, and as Weinandy would have us, so too as we approach the doctrine of impassibility.
His second majorly helpful contribution here, is simply to quote from the The Oxford Dictionary of the Christian Church and give us 3 elements of impassibility:
external passibility or the capacity to be acted upon from without, (2) internal passibility or the capacity for changing the emotions from within, and (3) sensational passiblity or the liability to feelings of pleasure and pain caused by the action of another being. (p38)
So, when we talk about impassibility, we are talking about God not being able to be acted upon from without, not being changeable by internal emotion, and not being subject to external sensation.
Chapter 3 is also very helpful. In it Weinandy covers the biblical terrain, with particular attention to the Old Testament. He notes the seemingly overwhelming evidence for a passible God (p58 for example), but proceeds in a different manner. He talks first about how God is known in the OT, through his saving and covenanting Presence. And yet this present God is known as the Creator of all, and so is wholly Other. Weinandy's point is that we cannot begin with abstract notions of transcendence/immanence (presence/otherness), because the Scriptures intertwine these two from the start: God's saving presence is precisely because of his Otherness, and his Otherness is known only through his Presence.
While God, in his complete otherness, is ontologically distinct from the created order, and thus from all other beings, yet he is able to bring into existence, be present to, and act within the created order as one who is ontologically distinct from the created order, and he is able to do so only because he is ontologically distinct. Moreover, he is able to do so, in his wholly otherness, without forfeiting his wholly in otherness in so doing. (p53)
When we come to the question of the rich emotional language of God we ask, 'What is this anthropomorphic language saying about God?' It is the wholly Other God who is so filled with passion. He already transcends the merely human. God’s otherness must guide our interpretation of the depths of God’s passionate passions. (p59) And likewise when we consider God changing his mind. We need a hermeneutical tool to bring consistency, otherwise we interpret statements of God's changing and unchangingness on the same flat level and they are contradictory. Rather, God’s changing of his mind is predicated/conditioned upon a change in the people involved.
The reaction of God expresses "his unchanging and unalterable love for his people and of his demand for moral rectitude" (p61);
the statement that God does change his mind expresses this unchangeable mind of God under circumstances which, under ordinary human conditions (if God were man), would demand that a change of mind take place, but in actual fact need not, because God, as the Wholly Other, is constant in his love, forgiveness, righteousness and justice. (p61)
The great strength of Weinandy's work, to begin with, is his ability to work with what is so often seen as a contradiction, and dichotomies, and carefully present a biblical vision that not only holds the two in tension, but draws them into each other and reveals to us that God's Passion and Impassibility are deeply intertwined and cannot be separated.