I think you are getting things pretty mixed up. You are speaking of it being a historical fact that God wanted Jews to mark themselves as belonging to God, then do you think God did not want gentiles to belong to Him? That makes no sense. Scripture tells us God wants all man to belong to Him.
So what do you make of the passage in Exodus when God was going to kill Moses because of the physical uncircumcision of his son? Yes, it may have been Moses' heart was uncircumcised also, but how would Zipporah's circumcising affect Moses heart? And wasn't Zipporah also a gentile?
Exodus 4:24 And it came to pass by the way in the inn, that the Lord met him, and sought to kill him. Then Zipporah took a sharp stone, and cut off the foreskin of her son, and cast it at his feet, and said, Surely a bloody husband art thou to me. So he let him go: then she said, A bloody husband thou art, because of the circumcision.
Deuteronomy seems to indicate a similar command to that in Jeremiah.
Deut 10:16 Circumcise therefore the foreskin of your heart, and be no more stiffnecked.
What is a "foreskin of the heart"? Is there an equivalent term we use today, like "a chip on his shoulder" or a "heart full of pride"? Does the trimming off of the specifically male skin represent a cutting off of the seed of Adam, so we belong only to Christ? What, if anything, does it have to do with the sinful nature? Pride? Baptism?