I cannot accept that. If God "gave up" some of His free will then He would change. God is not changeable, He is the Unchangeable, Constant.
He wouldn't be all powerful if He gave something up. So no, that is not correct either.
There is no Christian writer earlier (I take that to mean before the fragmentation of the single unified faith that existed until then) who says such a thing. God does not ask us to accept anything that contradicts reason. The very reason that he gave us in our intellect.
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No, the Creator is not in His Creation. Believing that He is, is pantheism, pre-Christian, pagan. The New-Agers love the idea.
If I, as a sculptor, create a sculpture, there is nothing of me in the sculpture, I lose nothing. If there was, I would be missing some fleshy bit, I would be changed, and not being God, I would die. To say there is something of me in the sculpture moves into the abstract, non-material realm. Even Shakespeare proved it in terms that the common folk could understand, in the Merchant of Venice, in that taking away a pound of flesh would deprive the man of his essence, and cause death.
Whereas humans can create something from something else, we cannot create something from nothing, only God can, and did, create something from nothing. That is the second reason, that your proposition is false. Whatever He did, when He created creation, He created it from nothing, He did not "give up" part of Himself, He remained absolutely Changeless. No Christian writer can make such a proposition. If one did, by that act, he would prove himself to be a heretic, a non-Chiristian.
On the relation to Theodicy. Since God is all Goodness, He cannot create evil (or extend His Will into something evil). He only allows evil.