Here he applies what he had laid down more generally to the believing Romans in particular.
Not in the flesh, but in the Spirit; i.e. not after the flesh, but after the Spirit, ( as in Rom_8:5), or not carnally, but spiritually minded.
If so be that; the conjunction here is causal, not conditional; it may be rendered, seeing that, or forasmuch as: see Rom_8:17,31 2Th_1:6.
The Spirit of God dwell in you; the Spirit of God dwells in the regenerate, not only by the immensity of his presence, so he is every where and in all things; but by the presence and efficacy of his grace. The indwelling of the Spirit in believers denotes two things:
1. His ruling in them: where a man dwells as Lord, there he doth command and bear rule.
2. His abiding in them, and that for ever, Joh_14:16.
If any man have not the Spirit of Christ, he is none of his; if he has not the same Spirit which in the former part of the verse is called the Spirit of God: it is called the Spirit of Christ, because it proceeds from him, and is procured by him, Joh_14:26Joh_16:7Gal_4:6. When he saith such a one is none of Christ’s, he means, that he doth not peculiarly belong to Christ, he hath no special interest in him, is no true member of him. As a merchant sets his seal upon his goods, so doth Christ his Spirit upon his followers, Eph_1:13.