But ye are not in the flesh, but in the Spirit, if so be that the Spirit of God dwell in you. Now if any man have not the Spirit of Christ, he is none of his.
When a person is born again, they are no longer in the flesh but in the Spirit. They live in a different sphere. They do not only live in the Spirit, but the Spirit lives in them. In fact, if they are not indwelt by the Spirit of Christ, they do not belong to Christ.