But if we have died, etc. He repeats this for no other end but that he might subjoin the explanation which follows, that Christ, having once risen, dies no more. And hereby he teaches us that newness of life is to be pursued by Christians as long as they live; for since they ought to represent in themselves an image of Christ, both by crucifying the flesh and by a spiritual life, it is necessary that the former should be done once for all, and that the latter should be carried on continually: not that the flesh, as we have already said, dies in us in a moment, but that we ought not to retrograde in the work of crucifying it. For if we roll again in our own filth, we deny Christ; of whom we cannot be the participators except through newness of life, inasmuch as he lives an incorruptible life.

This passage is a confirmation and illustration of what the apostle had said before, Romans 6:5-7. The argument is, that as Christ was once dead but now lives to God, and will no more die, so we, being dead to sin, but living unto God, should not obey sin, but should live only to God.

Now if we be dead with Christ - If we be dead in a manner similar to what he was; if we are made dead to sin by his work, as he was dead in the grave; see the note at Romans 6:4.
We believe - All Christians. It is an article of our faith. This does not refer to the future world so much as to the present. It becomes an article of our belief that we are to live with Christ.
That we shall also live with him - This does not refer primarily to the resurrection, and to the future state, but to the present. "We hold it as an article of our faith, that we shall be alive with Christ." As he was raised up from death, so we shall be raised from the death of sin. As he lives, so we shall live in holiness. We are in fact raised up here, and, as it were, made alive to him. This is not confined, however, to the present life, but as Christ lives forever, so the apostle goes on to show that we shall.

Now if we be dead with Christ - According to what is stated in the preceding verses. See particularly on the 5th verse (Romans 6:5 (note)).

Now if we be dead with Christ,.... This does not imply any doubt about it, but is rather a taking it for granted: seeing we are dead with Christ by union with him, as our head and representative, and by communion with him in the benefits of his death, and being planted together in the likeness of it; or being dead to the law, sin, and the world, through the virtue and efficacy of Christ's death:
we believe that we shall also live with him; not only a life of justification by faith in his righteousness; and a life of sanctification from him, and to his glory; the continuance of which, and a perseverance in it, are firmly believed; but a life of glory and happiness with him hereafter, both in the new Jerusalem, in the new heavens, and new earth, in the glorious state of the church on earth, and in heaven to all eternity; where they shall be personally and visibly with him, in soul and body, and shall live in the most intimate and uninterrupted communion with him, enjoying the highest pleasure, and the most consummate happiness; and are therefore under the greatest obligation, whilst here on earth, to live, not in sin, but to righteousness, and to his praise and glory; with whom they are now dead to sin, and with whom they not only hope, but believe they shall live throughout the endless ages of eternity.

Now if we be dead--"if we died."
with Christ, &c.--See on Romans 6:5.

Dead with Christ - Conformed to his death, by dying to sin.