What part about chosen before the foundation of the world and predestined don't you understand?No such Biblical teaching as you misunderstood it.
What it says, ". . . According as he hath chosen us in him before the foundation of the world, that we should be holy and without blame before him in love: Having predestinated us unto the adoption of children . . . ."
Romans 8:29, explained, ". . . For whom he did foreknow, he also did predestinate to be conformed to the image of his Son, . . ." Per 1 John 3:2, ". . . when he shall appear, we shall be like him; . . .". So the meaning of Romans 8:23.
Again how are we Son's far before we are ever adopted? Honestly, if we are son's...that means we are...adopted! How else could we, who are only able to be son's by being in Christ, be son's if we aren't already adopted?