John Calvin Commentary Romans 6:9

"knowing that Christ being raised from the dead dieth no more; death no more hath dominion over him." — Romans 6:9 (ASV)

Death no more rules over him, and so forth. He seems to imply that death once ruled over Christ; and indeed, when he gave himself up to death for us, he in a manner surrendered and subjected himself to its power; it was, however, in such a way that it was impossible that he should be kept bound by its pangs, so as to succumb to or be swallowed up by them. He, therefore, by submitting to its dominion, as it were, for a moment, destroyed it forever.

Yet, to speak more simply, the dominion of death is to be referred to the state of death voluntarily undergone, which the resurrection terminated. The meaning is, that Christ, who now gives life to the faithful by his Spirit, or breathes his own life into them by his secret power from heaven, was freed from the dominion of death when he arose, so that by virtue of that same dominion he might set free all his people.