Albert Barnes 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)

Knowing. As we all know. This is assumed as an undoubted article of belief.

Dieth no more. He will never die again. He will have occasion to make no other atonement for sin; for that which he has made is sufficient for all. He is beyond the dominion of death and will live for ever. Revelation 1:18: I am he that liveth and was dead, and behold I am alive for evermore. This is not only a consolation to the Christian, but it is an argument why he should be holy.

No more dominion. No rule; no lordship; no power. He is free from its influence; and the king of terrors cannot reach his throne. (Compare to Hebrews 9:26-28 and Hebrews 10:12).