Why do Christian theologians so-much want God to be "unchanging", when He obviously isn't and can't be?

It is a kind of obvious common sense that the Christian God must be responsive to us. 

And to respond is to change. 

Yet it is a Big Thing - and apparently has been since not-long-after the ascension of Jesus - that God should be unchanging, always the same. 

This is asserted all over the place among theologians, by Catholics and Protestants; yet it is clearly nonsense in terms of our relationship with God... So why is the idea such a dogmatic obsession?  

Why? To cut my answer short, the reason is that theologians are (and - it seems - always have been) captives of their own philosophical categories inherited from the ancient Greeks and Romans; which see the alternatives as a thing changing or not-changing, and can therefore see no way that God's identity as God can be maintained except by His never-changing. 

But this way of regarding identity is not the one which we were born believing, and not how we assume identity through time. 

Instead; we regard someone as staying the same person when they continuously exist.

My mother was my mother throughout her mortal life and beyond, despite whatever transformations her mind or body may undergo (development, ageing, dying, resurrection); so long as she continuously remains that person. 

She can respond to my needs; and be changed by these interactions - yet she still remains herself. 

Analogously; there is no reason to assume that God must not change in order to remain the entity, the being, the person that is God.  

What of nature, in particular of Goodness? There may be a concern that is God could change open-endedly in response to His interactions with Men and creation; then he might sooner-or-later cease to be Good? 

But that is only so in this mortal life, where our natures are partly sinful and our motivations are mixed. 

Christians believe that God is wholly Good by nature and in His motivations - and there is zero reason why God's characteristic and defining nature and motivations should change as a consequence of interactions - no matter how much God is changed by the interactions.  

As usual, I trace the problem down to fundamental metaphysical assumptions; and to the too-common inability to recognize when we are assuming, and when what is assumed could be different in reality. 

So long as people decide (assume) that all valid metaphysical possibilities have necessarily been captured by previous generations of philosophers and theologians, and our job as Christians is simply to choose between them -- then we remain trapped by their errors, omissions, limitations - and any differences in consciousness they had from us.

I contend that Men are spontaneously wiser than they realize, and in particular we come into this world with the divine gift of a broadly-correct understanding of its basic nature - for example, the assumptions that the world is alive and conscious ("animism"), and that our thinking interacts with the world. 

After all; why wouldn't God provide His children with broadly-correct assumptions built-in? 

It seems an obvious necessity. 

Thus ordinary Men have often been wiser than theologians; and lived Christianity truer and more-Good than than the often unloving, impersonal, Christianity of the theologians. 

Ordinary Christians have always known that God is changed by us, just as parents are changed by their children. This is not a problem - indeed it is absolutely necessary for the Christian God. A God who is not changed by His children is imaginable, and indeed such an understanding of God is common now and has-been through history. But this is not the Christian God.