I have no idea who told you this but I'm not a Calvinist and I do not believe that God elects gentiles before Salvation at all. The only ones that are elect before Salvation are Jews. and that election does not necessarily assure Salvation. Scripture does not say that any Gentile is elect.Here's the way I see it, and it makes no difference whether you see it from a Calvinist or non-Calvinist perspective/
The Calvinist believes God has chosen his own from the beginning. They will be saved, and there is no possibility that they will not, in time. Thus, in the mind of God, they are already sheep. It is correct that they are in a lost condition until they are saved. But there is no possibility that they will die in that condition. God will employ the means to bring them to repentance and faith.
The non-Calvinist holds that God chooses based on foreseen faith. God knows from eternity who will receive him by repentance and faith. There is no possibility that they won't. Thus, their salvation is assured from eternity. And in the mind of God, he may rightly call them His sheep.
Even if I could accept men being the sheep of God before Salvation. Someone would have to show me in scripture how we can belong to God and Satan at the same time. Christ said we cannot serve two masters. For me there is no doubt that before I submitted myself to Christ I belonged to Satan.So Jesus' reference to the "lost sheep" makes sense. They are not yet saved in time, but will be, thus he calls them sheep.
I disagree. God never changes as He has always been God almighty and always will be. How ever God is not limited to man's ideas of Him. Nor is His omnipotence. Nothing is impossible with God. Scripture could not say all things are possible with God and it not be so.Some of this is based on God's immutability and omnipotence. God doesn't change. he never has a new thought. What He knows today, He has always known. What He decides today, He has always decided.
Mat 19:26 But Jesus beheld them, and said unto them, With men this is impossible; but with God all things are possible.
Mar 14:36 And he said, Abba, Father, all things are possible unto thee; take away this cup from me: nevertheless not what I will, but what thou wilt.
MB