Romans 8:16-17; Romans 8:21; Romans 9:7-8

16 The Spirit itself beareth witness with our spirit, that we are the children of God: 17 And if children, then heirs; heirs of God , and joint-heirs with Christ; if so be that we suffer with him, that we may be also glorified together .
21 Because the creature itself also shall be delivered from the bondage of corruption into the glorious liberty of the children of God.
7 Neither, because they are the seed of Abraham, are they all children: but, In Isaac shall thy seed be called . 8 That is , They which are the children of the flesh, these are not the children of God: but the children of the promise are counted for the seed.