John Chrysostom

And indeed even before the crown, this is in itself the greater crown, the partaking with our Master. But he says, I give even another reward. Of what kind is it? It is life eternal. For "we believe," he says, "that we shall also live with Him." And whence is this clear?

Homily on Romans 11 ↗

Theophylact of Ohrid

Here, it would seem, there is a repetition of what was said; but in reality there is not. Above, the apostle said that we must always remain dead to sin, and now he reasons about the resurrection of the new life according to God, which we must always have. If through baptism we died with Christ, then we believe that we shall always have the resurrection belonging to us, consisting in the new life.

Commentary on Romans ↗

Thomas Aquinas

Then when he says, now, if we be dead, he clarifies the second effect by showing how it conforms one to the life of Christ. The reasoning is this: one who dies with the dying Christ also lives with the rising Christ. But Christ rose from the dead, in such a way that he will never die again. Therefore, one who has died to sin lives with the risen Christ in such a way that he has the faculty of never returning to sin. …

Commentary on Romans ↗