Romans 8:20 For the creature was made subject to vanity, not willingly, but by reason of him who hath subjected the same in hope,
21 Because the creature itself also shall be delivered from the bondage of corruption into the glorious liberty of the children of God.
it’s because our earthly bodies are foreign to who and what we are or have become in Christ when we were saved.
A righteous, holy (justified) person living in a corrupt body, in bondage to a body that is prone to another law.
The same earthly body which will be done away with once we meet the Lord in the air and receive our new celestial/glorified bodies.
The very reason –
3 For ye are dead, and your life is hid with Christ in God – Colossians 3:3.
2 Timothy 2:19 Nevertheless the foundation of God standeth sure, having this seal, The Lord knoweth them that are his. And, Let every one that nameth the name of Christ depart from iniquity.
When the world sees us, they don’t see SAVED, they see another human being with rotten flesh and would argue whether we are saved or not, even though we would tell them what we BELIEVE because unsaved people judge you by your flesh – they cannot see the innerman which is saved and sealed, who is hid with Christ in God.
A creature (saved, sealed, justified, reconciled to God) in the bondage of corruption (the flesh) whilst on this earth.